Focus events are useless when 'from' and 'to' are the same.  But when
this is the result of a (Un)GrabKeyboard request, we should always send
them, including when the window manager had previously used XSetInputFocus
to specify the focus on a window which happens to be now taking a grab.

This is notably needed for window manager using XI to always get keyboard
events even during grabs, so they can determine exactly when grabbing is
active.
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>