Reported by Christoph von Wittich.

We need GL_ARB_instanced_arrays to be able to take the fastest path and
that's already checked in draw_primitive.  Note that
GL_ARB_instanced_arrays provides glDrawElementsInstanced if
GL_ARB_draw_instanced is not supported so we don't need to explicitly
check for the latter.

Wined3d doesn't actually require the GLX extension for multisampling
at this point (while it does require FBOs).