Support and require Clutter 1.2

Support and require Clutter 1.2

- Specify a minimum version of clutter-1.2.0
 - Switch clutter branch in the moduleset to master
 - Replace deprecated cogl_texture/material_unref() with
   cogl_handle_unref()
 - Use cogl_clip_push_rectangle() rather than cogl_clip_push()
 - Replace cogl_check_extension() with strstr - should be
   accurate enough.

https://bugzilla.gnome.org/show_bug.cgi?id=610679