Bug#621854: fixed in upstream xorg 1.9rc5/1.8.99.905

[Alex <alustenberg@gmail.com>]

via patch Revert "dix: use the event mask of the grab for TryClientEvents."

http://cgit.freedesktop.org/xorg/xserver/patch/?id=1884db430a5680e37e94726dff46686e2218d525
http://lists.freedesktop.org/archives/xorg-announce/2010-July/001354.html

grabbutton would cause the input mask to be incorrectly applied.  this
is no longer an issue on my testing instance (xorg 1.10), but has now
cropped up on an old-stable -> stable upgrade (xorg 1.*mumble* -> 1.7)