Support (fallback) app menu in SSD

We now allow "appmenu" in the button layout to make synchronizing it
with GTK+'s client-side decorations easier, but as some people tweak
their settings to get in-window app menus even when using the shell,
actually pop up the app menu when the button is activated.

https://bugzilla.gnome.org/show_bug.cgi?id=730752

js/ui/windowManager.js

@@ -1163,8 +1163,8 @@ const WindowManager = new Lang.Class({
         this._tilePreview.hide();
     },
 
-    _showWindowMenu: function(shellwm, window, x, y) {
-        this._windowMenuManager.showForWindow(window, x, y);
+    _showWindowMenu: function(shellwm, window, menu, x, y) {
+        this._windowMenuManager.showWindowMenuForWindow(window, menu, x, y);
     },
 
     _startAppSwitcher : function(display, screen, window, binding) {