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.
This adds build infrastructure for unit testing the API library
using the serial test harness. TODO: this should be replaced with
the parallel test harness, as the automake documentation says the
serial harness is deprecated.
The first and last tests to be run are scripts to initialize the test
environment (an X session with a special -modulepath argument and
xorg.conf file to pick up x11glvnd) and tear it down after all unit
tests are run.
This also adds a placeholder directory for a fake vendor library
called "GLX_dummy", to be implemented later.
