[Piglit] libepoxy conversion

[Eric Anholt]

https://github.com/anholt/libepoxy/releases/tag/v1.0

I noticed one little bug in my last rebase, where a GLES1 alias being
missing (GLES1 aliases are generally not done at all in the upstream
xml, but I've had a couple of patches for them land so it's definitely
fixable).  I'll fix that in a v1.0.1 later, then we can drop the XXX
from that patch.

So far, I've used the library in piglit and in glamor.  I'm hoping to
conver the X Server indirect rendering soon (it really wants it).

Besides reviewing this series, I'd like some actual windows developers
to see if the binaries I uploaded actually work for them -- I'd like
things to be reasonable for them if possible, and this workflow for
generating binaries for releases is easy enough that I could happily
turn around epoxy releases whenever we need xml updates.