* clutter/clutter-main.c: Don't free the ClutterMainContext so
that the main loop can be restarted.
* clutter/eglx/clutter-backend-egl.c:
* clutter/eglnative/clutter-backend-egl.c: Register an atexit
handler which disposes the backend object so that we are still
guaranteed to call eglTerminate on GLES.