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

src/st/st-texture-cache.c

@@ -865,7 +865,7 @@ st_texture_cache_load (StTextureCache       *cache,
       else
         return COGL_INVALID_HANDLE;
     }
-  cogl_texture_ref (texture);
+  cogl_handle_unref (texture);
   return texture;
 }