Add dynamic dispatch for any calls to OpenGL functions.

Add dynamic dispatch for any calls to OpenGL functions.

Previously, fips code was making direct calls to OpenGL functions,
(such as glGenQueries, glBeinQuery, etc. within metrics.c). Some
OpenGL implementations do not export these symbols directly,
(expecting the application to instead look the symbols up via a call
to glXGetProcAddressARB or eglGetProcAddress).

The new fips-dispatch code added here does precisely that, (and adds
wrapper for both glXMakeCurrent and eglMakeCurrent in order to know
which GetProcAddress function should be called).

The dispatch code follows the model of piglit-dispatch, (available
under the same license as fips). Thanks to Eric Anholt for suggesting
following the same approach as piglit.