DRI3/Present fixes for XServers 1.16 and 1.17rc - (v2)

[Mario Kleiner]

Hi,

an updated set of patches to fix the bugs i found in the
xserver dri3/present implementation and one bug in intel-ddx
uxa/dri3/present implementation. Axel Davys comments made me
rethink my original xserver patch and the new solution is
simple and better and afaics how this was actually intended
to work in the server, the server properly using the present_check_flip
ddx driver function.

Patch 1/2 fixes and slightly improves DebugPresent() macros for
the server to avoid crashes at logout, compositor en/disable or
closing windows while flips are pending when the server is compiled
with debug macros on.

Patch 2/2 fixes the use of PresentOptionAsync for page-flipped present,
and makes Present working on nouveau without horrible tearing.

These patches apply to master, 1.17rc and 1.16.2. They were tested
on top of 1.16.2 with the dri3/present backends of nouveau master
(glamor and exa) and intel master (sna and fixed uxa) on single-display
and dual-display, also ran through my hardware timing test equipment.

Patch uxa/present is a required fix for intel-ddx uxa backend, so
intel_present_check_flip no longer lies to the server about its
capabilities.

Can the x-server patches please also be included into the 1.16 series?

thanks,
-mario