Fixes Issue #983.
This change fixes an issue where the iframe shim used on IE6/7 to
prevent scrollbars from peeking through is not being hidden properly
when setVisible(false) is called. This also changes PopupPanel's
setVisible implementation to rely on visibility: hidden instead of
display:none, which ensures that the PopupPanel's size is accurate
even while it is not visible.

Patch by: bobv
Review by: knorton



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@1007 8db76d5a-ed1c-0410-87a9-c151d255dfc7
3 files changed