actor: Revert the Transition/Actor leak fix

The original code inside ClutterActor that dealt with Transitions
stopping was written for the ::completed signal, thus the code was
correctly handling the lifetime of the instances; when we moved to the
::stopped signal, we assumed that it worked in the same way - with less
conditions to be checked, obviously, but fundamentally similar to the
::completed signal. Sadly, I screwed up the signal definition, and the
signal ended up calling our handlers, but not the default one that did
the cleanup and released references on the Animatable instance.

After fixing the Timeline::stopped signal, we can go back to the
previous code.

Thanks to Craig Hughes for the help in tracking down this mess.

https://bugzilla.gnome.org/show_bug.cgi?id=695158

clutter/clutter-actor.c

@@ -18539,6 +18539,9 @@ on_transition_stopped (ClutterTransition *transition,
 
   info = _clutter_actor_get_animation_info (actor);
 
+  /* we need copies because we emit the signal after the
+   * TransitionClosure data structure has been freed
+   */
   t_quark = g_quark_from_string (clos->name);
   t_name = g_strdup (clos->name);
 
@@ -18552,12 +18555,12 @@ on_transition_stopped (ClutterTransition *transition,
       g_object_ref (transition);
 
       /* this is safe, because the timeline has now stopped,
-       * so we won't recurse
+       * so we won't recurse; the reference on the Animatable
+       * will be dropped by the ::stopped signal closure in
+       * ClutterTransition, which is RUN_LAST, and thus will
+       * be called after this handler
        */
       g_hash_table_remove (info->transitions, clos->name);
-
-      /* we can release the reference here */
-      g_object_unref (transition);
     }
 
   /* we emit the ::transition-stopped after removing the