[Piglit] Support for waffle WGL and related cleanups

[Emil Velikov]

Hello list,

The series adds a piglit_wgl_framework based on my "Add WGL support 
to waffle" GSoC this summer. A sizeable chunk of the waffle code is not 
yet upstream, although I would expect that to change soon :P

All but patches 04, 10 and 11 should be safe to land even without waffle 
in place.

NOTE: I have broken the waffle API in a non-backwards compatible way 
and will update the above three to handle new and old waffle as soon
as waffle WGL lands upstream and the version is bumped.

FWIW, with this series and the latest one of waffle I can reliably 
lockup my nvidia GPU while running piglit on Windows 7 :)

This series can be found in branch 'waffle-WGL' at
https://github.com/evelikov/piglit

while the latest waffle wgl (+fixes) 'yet-another-round-of-msvc-fixes' 
at https://github.com/evelikov/waffle

Question, comments and reviews are greatly appreciated.

Cheers,
Emil