x11drv: One more fix for "stuck" ctrl, shift & alt.

[Tomas Carnecky]

Vitaliy Margolen wrote:
> Anything wrong with this patch? It does fix the "stuck alt" problem for
> games I use alt+tab on.
> 

I can confirm that this fixes the bug. This patch is very important for
me as I don't have to switch back and forth between desktop and WoW to
un-stuck they alt-key. This patch works fine and I don't see any
side-effects.

tom