Bug 1048984.1: Utility methods for managing texture pool returns.  Make sure tiles go back to the correct pool. r=nsilva
Bug 1048984.2: mOutstandingClients could have been temporarily incorrect in GetTextureClient() call. Call ShrinkToMaximumSize() instead of ShrinkToMinimumSize() in ReturnDeferredClients().  Also add comments and more asserts around outstanding clients. r=nsilva