A few of my programs were using the client string in addition to the
main extensions string to see if a feature was present. Correct this to
only check for the currently available and working extensions.
Add OML_sync_control support, along with a simple program for testing
it. This means adding support for the DRI2GetMSC, DRI2WaitMSC and
DRI2WaitSBC requests.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>