Bug 1395 - apply and get_nth_actor are inconsistent

Bug 1395 - apply and get_nth_actor are inconsistent

When calling clutter_behaviour_apply() the new actor is prepended
to the list of actors to which a behaviour is applied; this breaks
the rest of methods working on the actors list, e.g.:

  # adding actors
  apply(actor_0);
  apply(actor_1);
  apply(actor_2);

  # expected: [ actor_0, actor_1, actor_2 ]
  [ actor_2, actor_1, actor_0 ] = get_actors();

  # expected: actor_2
  actor_0 = get_nth_actor(2);

This commit fixes the inconsistency in the returned values.