Implement a fake glXChooseVisual() and glXCreateContext() function for
use with the makecurrent tests. Likewise, implement
glMakeCurrentTestResults(), glBegin(), and glEnd().
Implement a fake glXGetClientString() for use with the getclientstr
test.
This vendor library will be loaded by the API library in various
subtests in the test suite, and will implement the bare minimum
needed to verify features and code paths in the API library. This
includes creating a fake GL "context", making current to the
"context", and calling some GL functions.
