xlib: call register_with_display() in Fake_glXChooseFBConfig()

as we do in Fake_glXChooseVisual().  This registers the MesaGLX
extension on the display so we can clean up buffers, etc. when
the display connection is closed.

Fixes a bug reported by Wayne E. Robertz.

NOTE: This is a candidate for the 7.11 branch.

Reviewed-by: Adam Jackson <ajax@redhat.com>

src/mesa/drivers/x11/fakeglx.c

@@ -1983,6 +1983,9 @@ Fake_glXChooseFBConfig( Display *dpy, int screen,
 {
    XMesaVisual xmvis;
 
+   /* register ourselves as an extension on this display */
+   register_with_display(dpy);
+
    if (!attribList || !attribList[0]) {
       /* return list of all configs (per GLX_SGIX_fbconfig spec) */
       return Fake_glXGetFBConfigs(dpy, screen, nitems);