x11: Handle all XI2 crossing mode values in switch

This fixes potential assertions if a GTK+ app gets to receive
a XINotifyPassiveGrab/Ungrab pointer crossing event, currently
triggerable by XIGrabEnter passive grabs.

http://bugzilla.gnome.org/show_bug.cgi?id=719762
x11: Handle XINotifyPassiveGrab/Ungrab in focus events

The focus handling code is shared between core and XI2 implementations,
so just handle the extra XI2 types for passive grabs. Those must be dealt
with in the same way than active grabs. Focus events with this crossing
mode could happen currently through the XIGrabFocusIn passive grab.

https://bugzilla.gnome.org/show_bug.cgi?id=719762