Fixes issue #1225.
Fixes a problem where Image.setUrlAndVisibleRect would not properly change
state if only the URL changed due to a typo.

Patch by: rdayal
Suggested by: Konstantin.Scheglov
Review by: knorton


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@1186 8db76d5a-ed1c-0410-87a9-c151d255dfc7