in Decoration, remove windows that are precisely hidden underneath other windows.
in Decoration, remove windows that are precisely hidden underneath other windows.

This is needed for WindowNavigation to work properly with the new
Decorations framework.

darcs-hash:20080204005413-72aca-7aa06211c7080d3d4f485017183251e3e6f440ab

yzhou61/xmonad-contrib,yzhou61/xmonad-contrib,yzhou61/xmonad-contrib