Fixes issue #1456; map entries now correctly write-through to the underlying map, and also reflected changes in the underlying map. This fixes HashMap and IdentityHashMap. Also adds tests for this behavior. Found by: nlwillia Review by: tobyr git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@2475 8db76d5a-ed1c-0410-87a9-c151d255dfc7