Fixes Issue #411.
PopupPanel in autohide mode now hides itself when it sees an outside mousedown
event to prevent it from immediately closing in the case where the panel was
opened from within a mousedown handler.

Patch by: bobv
Review by: knorton



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@992 8db76d5a-ed1c-0410-87a9-c151d255dfc7