[Piglit] Plan for enabling more tests in concurrent mode

[Chris Forbes]

Hello

I sent in a pile of random patches some time ago working toward having
more of the tests support -fbo. This is important on WMs which don't
give you the size you ask for [pretty much any tiling WM].

I realize that was a bit chaotic, so I'm starting over, making the
following changes:

- glutSwapBuffers gets replaced with piglit_present_results, and moved
to the right place if it's somewhere odd [there's a couple of cases
where pixels get read after the buffer swap, which seems bogus].

- unguarded glutKeyboardFunc moved to being consistently conditional
on !piglit_automatic. In most cases there is already a suitable block
because the test emits some keyboard instructions in non-automatic
mode

- use of glutReshapeFunc converted to appropriate piglit_*_projection
in piglit_display

And some tidiness things:

- spurious glFlush/glFinish removed

- raw glReadPixels converted to piglit_probe_*

- handrolled version checks converted to piglit_require_gl_version


Things I've yet to tackle:

- there's a few random tests which don't use the framework at all
(texline is particularly weird, unused and perhaps just broken now?)
- glean tests -- it would be nice if these could be run offscreen, but
will take some more doing
- it seems that the testrunner can jam at the end of the run, in some
rare cases. This gets worse with more concurrent tests.
- the choice of projections varies wildly between tests

Will follow up with actual patches shortly, and would appreciate
feedback on whether this is a sensible thing to do / traps / how to do
this for glean / etc.

Cheers

-- Chris