1 MULTI-LOBE FILTER BAG PRINCIPALLY FOR A POOL CLEANER REFERENCE TO PROVISIONAL APPLICATION This application is based on and hereby refers to U.S. Provisional Patent Application Serial No. 60/837,171, filed August 11, 2006, and having the same title as appears above, the entire contents of which provisional patent application are incorporated herein by this reference. TECHNICAL FIELD The present disclosure relates to debris filters and more particularly, although not necessarily exclusively, to filter bags for swimming pool cleaners. BACKGROUNDART U.S. Patent No. 5,863,425 to Herlehy, et al. illustrates a conventional filter bag for use with certain automatic pool cleaners. As disclosed in the Herlehy patent, the bag may be mounted onto a suction mast of a pool cleaner. Debris laden water is drawn through the suction mast into a mouth of the filter bag, with the bag capturing much of the debris while allowing the drawn water to pass through its porous material. The bag further may include a divider seam defining a rear pocket and a rear seam that may be separated when desired to facilitate removal of debris collected in the rear pocket. A clip may be used to connect the bag to an associated pressure hose to inhibit collapse of the bag under certain conditions. U.S. Patent No. 6,908,550 to Silverstein details another filter bag. Generally similar to the bag of the Herlehy patent, that of the Silverstein patent includes a mouth, a divider seam, and a separable rear seam in the form of a zipper. The Silverstein patent also discloses using a loop attached to the bag for connecting it to a pressure hose for stability. Described in U.S. Patent Publication No. 2005/02363 10 of Meritt-Powell is yet another filter bag of the types disclosed in the Herlehy and Silverstein patents. The bag of the Meritt-Powell publication includes, among other things, a divider 5581083_1 (GHMatters) P80100.AU.2 2 seam defined by a spaced series of welds. It also incorporates a ported tab at an upper end for engaging a support member in turn connecting to a pressure hose. According to the Meritt-Powell publication: the support member engages with the integral tab to prevent the filter bag from draping downwardly over and about the pool cleaner where the bag could otherwise become entangled in the cleaner wheels and/or scrape against pool surfaces. See Meritt-Powell Publication, p. 4, T 0031, 11. 22-26 (numerals omitted). U.S. Patent No. 7,029,583 to Meritt-Powell, finally, depicts filter bags with improved support members in the form of hose clasps. Such clasps, like other support members, tend "to prevent the bag from falling and draping downwardly over the pool cleaner." See Meritt-Powell Patent, col. 2, 11. 35-36. Need for the clasps exists because prior component wear in combination with prolonged exposure to water, sun and chemicals in a swimming pool environment can result in inadvertent separation of the filter bag from the supply hose particularly in response to increased weight attributable to collected debris. In addition, such removable support devices are often removed with the filter bag each time the bag is removed to discard the debris accumulated therein, whereby the removable support device is sometimes misplaced or inadvertently thrown away with the discarded debris. See id., 11. 43-52. The contents of the Herlehy, Silverstein, and Meritt-Powell patents and of the Meritt-Powell publication are incorporated herein in their entireties by this reference. SUMMARY OF THE DISCLOSURE Disclosed herein is a filter bag through which water may flow. The filter bag comprises means for attachment to a portion of a swimming pool cleaner, and a divider defining, at least in part, a flow path for debris-laden water entering the filter bag. The filter bag further comprises at least first and second pockets configured to receive debris too large to exit the filter bag when in use. Each of the first and second pockets define part of a respective first and second lobe, with 5581083_1 (GHMatters) P80100.AU.2 3 each lobe configured for opening at a rear margin thereof independent of the other lobe so as to facilitate emptying of debris from its respective pocket. The present disclosure provides alternate designs for filter bags similar to the types of bags described in the preceding section of this application. Unlike conventional filter bags, which include a single rear pocket behind the divider seam, bags of the present disclosure incorporate at least two such pockets rearward of the divider. Accordingly, the present bags have a substantially greater volume for retaining debris, reducing the frequency at which they must be emptied. The dual-lobe structure of preferred embodiments additionally provides a bag configuration symmetric rearward of the divider seam. This structure provides improved water flow and drag characteristics for cleaners and increases the total area of the openings through which water may pass, thereby reducing back pressure to which the debris-collection components of the cleaners are subjected in use. The lobes, further, may effectively capture an associated hose if desired to facilitate connection of the bag thereto. If, for example, the lobes themselves are fitted with complementary hook-and-loop (Velcro) fasteners, they may be fastened together so as to surround a position of the hose. This approach avoids the need for any separate hose-grasping component. Alternatively or additionally, a conventional loop, clamp, or other device may be used to connect the bag to the associated hose. Each lobe of the bag advantageously may be emptied independently of the other lobes. Accordingly, each lobe may include a separable rear (or other) seam to permit its being opened alone. Bags of the present disclosure may include cuffs or similar structures permitting their attachment to suction masts of automatic pool cleaners. They may be formed of nylon or other porous mesh material. A seam internal to the bag may connect forward portions of the lobes, and conventional external seams may form top, bottom, and forward boundaries or margins of the filters. Dual- or multi-lobe filter bags are disclosed herein. Additionally, filter bags with more than one pocket for retaining debris are disclosed herein. Filter bags symmetric rearward of a divider seam are also disclosed herein. 5581083_1 (GHMatters) P80100.AU.2 4 Further, filter bags with both increased debris-containing volume and increased total area of openings through which water may flow are disclosed herein. There are also filter bags whose lobes may be fastened around a section of an associated hose disclosed herein. Moreover, filter bags whose multiple debris-containing pockets may be opened independently to facilitate removal of contained debris are also disclosed. Also disclosed herein is a water-permeable filter bag. The filter bag comprises first and second primary walls, first and second secondary walls, and a divider seam interconnecting all of the first and second primary walls and the first and second secondary walls. The filter bag further comprises means for attachment to a portion of a swimming pool cleaner. The first and second primary walls are connected to define a front margin. The first primary wall and the first secondary wall form a first lobe including a first pocket rearward of the divider seam and configured to receive debris. The second primary wall and the second secondary wall form a second lobe including a second pocket rearward of the divider seam and configured to receive debris. Each lobe is configured for opening at a rear margin thereof independent of the other lobe so as to facilitate emptying of debris from its respective pocket. Also disclosed herein is an automatic swimming pool cleaner. The automatic swimming pool cleaner comprises a body and a filter bag. The filter bag comprises a divider defining, at least in part, a flow path for debris-laden water entering the filter bag, and at least first and second pockets configured to receive debris too large to exit the filter bag when in use. Each of the first and second pockets define part of a respective first and second lobe, with each lobe configured for opening at a rear margin thereof independent of the other lobe so as to facilitate emptying debris from its respective pocket. The cleaner further comprises means for attaching the filter bag to the body. BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms which may fall within the scope of the filter bag and automatic swimming pool cleaner as defined in the Summary, 5581083_1 (GHMatters) P80100.AU.2 5 specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: FIG. 1 shows a side elevational view of an exemplary filter bag of the present disclosure; FIG. 2 shows a top plan view of the filter bag of FIG. 1 illustrating its dual lobe structure as in use; and FIG. 3 shows a rear elevational view of the filter bag of FIG. 1 showing the lobes fully extended. DETAILED DESCRIPTION Depicted in FIGS. 1-3 is exemplary bag 10 of the present disclosure. Bag 10 preferably is to be used with an automatic pool cleaner, such as those shown or referenced in any of the Herlehy, Silverstein, or Meritt-Powell patents or the Meritt-Powell publication. Use of the filter bag is not necessarily so limited, however, as bag 10 conceivably could be utilized elsewise as appropriate or desired. Bag 10 advantageously comprises primary walls 14 and 18 and secondary walls 22 and 26. Each of walls 14, 18, 22, and 26 may be formed of one or more sheets or pieces of porous material. In use, water should be able to pass through walls 14, 18, 22, and 26, whereas most or all debris entrained in the water should not. As a result, bag 10 may serve to filter debris from flowing water and retain the filtered debris within the confines of walls 14, 18, 22, and 26. Sheets forming primary walls 14 and 18 are generally complementary in shape. Walls 14 and 18 are connected to define front margin 30 extending from a generally open lower bag mouth 34 to approximately the top 38 of bag 10. Front margin 30 preferably is curved as shown in FIG. 1. Front margin 30 need not necessarily be curved, however, nor if curved need it be curved in the manner depicted in FIG. 1. Bag mouth 34 may be created by not interconnecting forward lower edges of walls 14 and 18. FIG. 1 illustrates forward lower edge 42 of wall 14; a similar edge exists for wall 18. Instead, forward lower edge 42 and the corresponding edge of wall 18 may be connected to cuff 46 designed for direct or indirect 5581083_1 (GHMatters) P80100.AU.2 6 attachment to, preferably, a suction mast of a pool cleaner. Thus, as so mounted, the entirety of bag 10 is intended to extend above the suction mast. Unlike conventional bags, bag 10 includes two top margins 50 and 54 and two bottom rear margins 55 and 56. Top margin 50 may be formed by connecting primary wall 14 with secondary wall 22 at top 38 of bag 10. Top margin 54, by contrast, may be formed by connecting primary wall 18 with secondary wall 26 at top 38. Bottom rear margin 55 is formed by connecting primary wall 14 with secondary wall 22 at bottom 57 of bag 10, and bottom rear margin 56 is created by connecting walls 18 and 26 at bottom 57. Primary wall 14 and secondary wall 22 additionally may be interconnected to form one rear margin 58 at rear 62 of bag 10. A second rear margin 66, also at rear 62, may be created by connecting primary wall 18 and secondary wall 26. Portions of walls 14 and 22 forming rear margin 58 may be fitted with hook-and loop fasteners, as may portions of walls 18 and 26 forming second rear margin 66. Accordingly, walls 14 and 22 form a first lobe 70 that may be opened at rear margin 58, whereas walls 18 and 26 form a second lobe 74 that may be opened at second rear margin 66. FIGS. 2-3 illustrate optional loop 78. If present, loop 78 preferably, but not necessarily, may be connected to top margin 54 (or top margin 50) adjacent seam 82 connecting forward edges 86 and 90 of respective secondary walls 22 and 26. Loop 78 additionally may be comprised of strips 94 and 98 adapted to be fastened together (to form loop 78) and unfastened (so as to be placed around a suction mast or other supporting object). In a preferred version of loop 78, strips 94 and 98 contain complementary hook-and-loop fasteners. Alternatively, the loop fastener of loop 78 may be connected instead to second rear margin 66 of second lobe 74, with the corresponding hook fastener being connected to rear margin 58 of first lobe 70 (or vice-versa), so that the hook and-loop fasteners are in shear as lobes 70 and 74 pull apart during debris fill. This configuration allows lobes 70 and 74 to surround or capture a hose or other object and help to maintain the upright and symmetrical position of bag 10. As yet another alternative, the hook-and-loop fasteners may be configured to create a tensile joint as lobes 70 and 74 pull apart during fill. As the lobes 70 and 74 fill, 5581083_1 (GHMatters) P80100.AU.2 7 the complementary hook portion and loop portion of the fasteners could detach to provide visual indication of the filled state of lobes 70 and 74. Divider seam 102 extends upward from bottom 57 of bag 10 but terminates prior to top 38. Seam 102 interconnects all of walls 14, 18, 22, and 26, defining a primary fluid flow path 106 from mouth 34 upward through forward section 110 of bag 10. Seam 102, further, preferably is generally coincident with (although shorter than) seam 82. To the rear of seam 102 are thus two debris-containing pockets 114 and 118. As debris-laden water flows along path 106 through bag 10, debris too large to exit the bag 10 eventually will settle (under gravity) into either of pockets 114 or 118. The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present disclosure. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the disclosure. The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the filter bag and automatic swimming pool cleaner as disclosed herein. In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the filter bag and automatic swimming pool cleaner. 5581083_1 (GHMatters) P80100.AU.2