[Mesa-dev] Fix and cleaned up testcase

[Eric Anholt]

There was stuff in the testcase that looked quite unusual (red instead
of green for success, not showing all the results at once, etc.) for a
piglit test, so I hacked up the testcase quite a bit.  It was an
interesting bug, and luckily an easy little fix.

I'd love to get your review/ack on the testcase changes, and hopefully
someone else can look at the Mesa change.