Fixes PopupImplIE6 to keep their IFrame shims' z-index tied to their associated PopupPanels. Issue: 1279 Patch by: mat.gessel Review by: ajr, jgw git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@2449 8db76d5a-ed1c-0410-87a9-c151d255dfc7