It is not always required to do a full repaint in each frame. E.g. in sliding popups the repaint areas are known and tracked.
This change reduces the painting overhead to just the window area.
Nevertheless I consider this change as experimental and will revert the commit in case it introduces rendering glitches.
Other effects which are good candidates for this flag is wobbly windows, magic lamp, minimize or in general all effects which transform just one window.
svn path=/trunk/KDE/kdebase/workspace/; revision=1158838
6e31461039