Fix Popup animations in RTL mode. We want to animate from the upper-right corner down to the lower-left corner (in LTR mode, the animation goes from the upper-left corner to the lower-right corner).

Patch by: adil.allawi, rdayal
Review by: jlabanca

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@2405 8db76d5a-ed1c-0410-87a9-c151d255dfc7