glx/dri3: Request non-vsynced Present for swapinterval zero. (v3)

glx/dri3: Request non-vsynced Present for swapinterval zero. (v3)

Restores proper immediate tearing swap behaviour for
OpenGL bufferswap under DRI3/Present.

Cc: "10.3 10.4" <mesa-stable@lists.freedesktop.org>
v2: Add Frank Binns signed off by for his original earlier
patch from April 2014, which is identical to this one, and
Chris Wilsons reviewed tag from May 2014 for that patch, ergo
also for this one.

v3: Incorporate comment about triple buffering as suggested
by Axel Davy, and reference to relevant spec provided by
Eric Anholt.

Signed-off-by: Frank Binns <frank.binns@imgtec.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Axel Davy <axel.davy@ens.fr>
Reviewed-by: Eric Anholt <eric@anholt.net>