GetWindowDC paints in nonclient area (not recommended on msdn)
and not needed for skins. Also, it doesn't take WS_CLIPCHILDREN
into account and forced to add a lengthy hack which can now be removed.

This patch hopefully could also fix a refresh issue found only on
Vista/Win7 (to be tested) (http://forum.videolan.org/viewtopic.php?f=15&t=68891)