glx: only advertise GLX_INTEL_swap_event if it's supported

Only drivers supporting DRI2 version >=4 support GLX_INTEL_swap_event.
So lets mark it as such otherwise applications which use this extension
(i.e. everything based on Clutter, e.g. gnome-shell) break horribly on
drivers supporting DRI2 versions only up to 3.

Note: This is a candidate for the 9.0 branch.

Reviewed-by: Brian Paul <brianp@vmware.com>
1 file changed