dix: always send focus event on grab change

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>

dix/enterleave.c

@@ -1562,7 +1562,7 @@ DoFocusEvents(DeviceIntPtr pDev, WindowPtr from, WindowPtr to, int mode)
     if (!IsKeyboardDevice(pDev))
         return;
 
-    if (from == to)
+    if (from == to && mode != NotifyGrab && mode != NotifyUngrab)
         return;
 
     CoreFocusEvents(pDev, from, to, mode);