Using this we clear the global state thus the user can call waffle_init()
multiple times, as things won't get clobbered.
According to gl_basic we cleanup ~20K of leaks (still reachable) and catch
a bug in the GL/dri2 loader :-)

Before:
    definitely lost: 63 bytes in 4 blocks
    still reachable: 43,695 bytes in 116 blocks

After:
    definitely lost: 87 bytes in 5 blocks
    still reachable: 23,451 bytes in 55 blocks

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>