glx: Fix interval test in glXSwapIntervalMESA

It appears that, in spite of what the spec says, the interval
parameter to glXSwapIntervalMESA has been an unsigned int since
day-1.  This made the 'if (interval < 0)' test useless.  The test is
removed and the spec is updated to note that the interval is an
unsigned value.
2 files changed