On linux, the GSource func attached to the clutter_threads_add_idle
was not getting the cpu ressource periodically.
Because the use of clutter_threads_enter/leave inside the fakesink
callback seems to be too strong.
So remove the use if clutter_threads_enter/leave in the fakesink callback.
Then replace GQueue by GAsyncQueue to keep thread safe access to the
communication queues between clutter and gst-gl.
Call clutter_threads_add_idle with high priority.
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
