[animation] add varargs support for signal::completed

Added support for registering a handler for the completed signal
directly amongst the varargs making it easier to attach code
to be executed when animations complete.

clutter/clutter-animation.c

@@ -1421,6 +1421,15 @@ clutter_animation_setup_valist (ClutterAnimation *animation,
       GValue final = { 0, };
       gchar *error = NULL;
 
+      if (G_UNLIKELY (g_str_equal (property_name, "signal::completed")))
+        {
+          GCallback callback = va_arg (var_args, GCallback);
+          gpointer  userdata = va_arg (var_args, gpointer);
+
+          g_signal_connect (animation, "completed", callback, userdata);
+        }
+      else
+        {
           if (g_str_has_prefix (property_name, "fixed::"))
             property_name += 7; /* strlen("fixed::") */
 
@@ -1446,6 +1455,7 @@ clutter_animation_setup_valist (ClutterAnimation *animation,
           clutter_animation_setup_property (animation, property_name,
                                             &final,
                                             pspec);
+        }
 
       property_name = va_arg (var_args, gchar*);
     }
@@ -1627,6 +1637,26 @@ clutter_actor_animate_with_timeline (ClutterActor    *actor,
  * to control the animation or to know when the animation has been
  * completed.
  *
+ * If a name argument starts with "signal::" the two following arguments are
+ * used as callback function and userdata for a signal handler installed on the
+ * #ClutterAnimation object, for instance:
+ *
+ * |[
+ *
+ *   static void
+ *   on_animation_completed (ClutterAnimation *animation,
+ *                           ClutterActor     *actor)
+ *   {
+ *     clutter_actor_hide (actor);
+ *   }
+ *
+ *   clutter_actor_animate (actor, CLUTTER_EASE_IN, 100,
+ *                          "opacity", 0,
+ *                          "signal::completed", on_animation_completed, actor,
+ *                          NULL);
+ * ]|
+ *
+ *
  * Calling this function on an actor that is already being animated
  * will cause the current animation to change with the new final values,
  * the new easing mode and the new duration - that is, this code: