appMenu: Disable app menu during startup animations

When activating the app menu while displaying a startup notification
animation, the application shown in the menu does not match the
application providing the menu. To avoid this case, make the menu
button unreactive while playing the animation.

https://bugzilla.gnome.org/show_bug.cgi?id=672322

js/ui/panel.js

@@ -346,6 +346,7 @@ const AppMenuButton = new Lang.Class({
             return;
 
         this._stop = true;
+        this.actor.reactive = true;
         Tweener.addTween(this._spinner.actor,
                          { opacity: 0,
                            time: SPINNER_ANIMATION_TIME,
@@ -360,6 +361,7 @@ const AppMenuButton = new Lang.Class({
 
     startAnimation: function() {
         this._stop = false;
+        this.actor.reactive = false;
         this._spinner.actor.show();
     },