DRI2: Don't disable GLX_INTEL_swap_event unconditionally

DRI2: Don't disable GLX_INTEL_swap_event unconditionally

GLX_INTEL_swap_event is broken on the server side, where it's
currently unconditionally enabled. This completely breaks
systems running on drivers which don't support that extension.
There's no way to test for its presence on this side, so instead
of disabling it uncondtionally, just disable it for drivers
which are known to not support it. It makes sense because
most drivers do support it right now.
We'll be able to remove this once Xserver properly advertises
GLX_INTEL_swap_event.

Note: This is a candidate for stable branch branches.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=60052
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
Tested-by: Ian Romanick <ian.d.romanick@intel.com>