ctrlAltTab: Fix external DOCK windows

We always add external DOCK windows to the ctrl-alt-tab switcher,
e.g. separate dock applications or nautilus' desktop windows.
Since commit 1f46a0dc26, all items in the switcher are expected
to set a proxy parameter, but the aforementioned code was not
updated accordingly.

https://bugzilla.gnome.org/show_bug.cgi?id=695395

js/ui/ctrlAltTab.js

@@ -103,6 +103,11 @@ const CtrlAltTabManager = new Lang.Class({
                 else
                     icon = textureCache.bind_pixbuf_property(windows[i], 'icon');
                 items.push({ name: windows[i].title,
+                             proxy: windows[i].get_compositor_private(),
+                             focusCallback: Lang.bind(windows[i],
+                                 function(timestamp) {
+                                     Main.activateWindow(this, timestamp);
+                                 }),
                              iconActor: icon,
                              sortGroup: SortGroup.MIDDLE });
             }