shell-gtk-embed: Make the MetaWindowActor for a tray icon unreactive

The MetaWindowActor isn't painted, and we empty its input shape in
the X scene graph, but Clutter still picked it. Set it as unreactive
so that it can't be picked.

https://bugzilla.gnome.org/show_bug.cgi?id=706536

src/shell-gtk-embed.c

@@ -106,6 +106,9 @@ shell_gtk_embed_window_created_cb (MetaDisplay   *display,
                                              0, 0 /* offset x/y */);
       cairo_region_destroy (empty_region);
 
+      /* Set the actor as unreative so Clutter doesn't pick it, either */
+      clutter_actor_set_reactive (window_actor, FALSE);
+
       gdk_window_lower (gdk_window);
 
       /* Now that we've found the window we don't need to listen for