dix: Set focus field on XI2 crossing events

dix: Set focus field on XI2 crossing events

Set on DeviceEnterLeaveEvent() the xXIEnterEvent->focus field
similarly to how the CoreEnterLeaveEvent() function above does
for core events.

This fixes bug https://bugzilla.gnome.org/show_bug.cgi?id=677329
reported to GTK+, where focus handling on window managers with
sloppy focus or no window manager present was broken due to this
field being always set to FALSE.

Signed-off-by: Carlos Garnacho <carlosg@gnome.org>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>