[PATCH 0/3] present: Minor present extension fixes

[Keith Packard]

Here are three minor Present extension fixes. Review would be
appreciated, as always. These are also available on my present-fixes
branch at:

	git://people.freedesktop.org/~keithp/xserver.git

Avoid judder when using fake MSC counters (for drivers without vblank hooks):

 [PATCH 1/3] present: Round fake MSC computations intead of truncating

Avoid issues with buggy drivers:

 [PATCH 2/3] present: Ignore event_id 0 from driver vblank notify

Prevent segfault on client exit:

 [PATCH 3/3] present: Signal destroyed flip window with vblank->window

-keith