Fixes UISuite failures (DOMTest and PopupTest).
r2133 changed the behavior of RootPanel such that position:relative
and overflow:hidden would be added to the underlying element. I
also rolled back the test changes in r2156 since this change was the root
cause of those failures.

Review: jgw (TBR)



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@2167 8db76d5a-ed1c-0410-87a9-c151d255dfc7