* clutter/clutter-actor.c:
* clutter/clutter-actor.h:
Clean up of parenting code (see #972)
Doc updates to section intro.
Add clutter_actor_allocate_preferred_size () utility call
* clutter/clutter-group.c: (clutter_fixed_layout_allocate):
Use clutter_actor_allocate_preferred_size ()
* doc/clutter-actor-invariants.txt:
Add some more notes
* doc/clutter-actor-invariants.txt: Document the flags, the
invariants, the state changes and the minimum requirements for
actor implementations. Needs to be tweaked and fleshed out
before 0.8.0, and we obviously need to enforce the invariants.