* clutter/clutter-actor.c:
* clutter/clutter-actor.h:
* clutter/clutter-clone-texture.c:
* clutter/clutter-private.h:
* clutter/clutter-texture.c:
* clutter/x11/clutter-x11-texture-pixmap.c:
Attempt to lower overhead of updating TFP's (particularly mipmaped).
Compresses mipmap updates only for visible TFPs.
Avoiding updates for non visible TFP's whilst keeping visible
clones working ok.