It requires at least clutter 0.8.6 since lower clutter versions are
not compatible with GL_TEXTURE_RECTANGLE_ARB.
Remove use of ClutterEffectTemplace since it does not exist in
clutter 0.9.
The external opengl context must be specify when creating
our OpenGL context (glx) or just after (wgl).
When calling glXCreateContext or wglShareLists, the
external opengl context must not be current.
Then our gl context can be current in the gl thread while
the external gl context is current in an other thread.
See tests/examples/clutter/cluttershare.c