dix: call UpdateDeviceState() for emulated TouchEndEvents

ProcessTouchEvents() calls UDS for all touch events, but if the event type
was switched to TouchUpdate(pending end) UDS is a noop.

Daniel Drake found this can cause stuck buttons if a touch grab is
activated, rejected and the touch event is passed to a regular listener.
This sequence causes the TouchEnd to be changed to TouchUpdate(pending end).

The actual TouchEnd event is later generated by the server once it is passed
to the next listener. UDS is never called for this event, thus the button
remains logically down.

A previous patch suggested for UDS to handle TouchUpdate events [1], however
this would release the button when the first TouchEvent is processed, not
when the last grab has been released (as is the case for sync pointer
grabs). A client may thus have the grab on the device, receive a ButtonPress
but see the button logically up in an XQueryPointer request.

This patch adds a call to UDS to TouchEmitTouchEnd(). The device state must
be updated once a TouchEnd event was sent to the last grabbing listener and
the number of grabs on the touchpoint is 0.

[1] http://patchwork.freedesktop.org/patch/13464/

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

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