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Bringup is really not flying when I can't see anything.  So dump back
to all software so I can turn on a bit at a time.

This should avoid a bunch of absurdity with GLX front buffer handling,
fix exposes, and improve performance.  For now we're copying the whole
buffer while glamor is developed.

This brings in idr's glu3 code.  We'll probably want to move to linking to
it as a library, once an ABI-stable release is out.

This fixes segfaults on starting gnome-terminal.