[Piglit] [PATCH v2 0/2] Revised isinf/isnan test

[Paul Berry]

This is a revised isinf/isnan test based on Ian's comments--the core
functionality is unchanged.  The new test makes use of multiple
compilation units instead of string substitution in all places except
one (when constructing the compute_value() function--in this one case
I think it makes the code more readable).

In addition I made the use of "static" consistent, explained the
counterintuitive use of the "z" uniform, and made the test require GL
3.0 rather than being unnecessarily tricky with extensions.
Surprisingly, there wasn't a convenient utility function for requiring
a certain GL version (like there is for GLSL), so I added that in a
separate patch.

All variants of the test now pass on nVidia's proprietary Linux
driver.

[PATCH v2 1/2] Add a piglit_require_GL_version() function.
[PATCH v2 2/2] Add a test of isinf() and isnan() functionality.