Use shellwm.takeover_keybinding for Alt-F1 and Alt-F2

This fixes a regression where we weren't using the correct event
timestamps, because for both of these we were sending an XClientMessage
to ourself.

https://bugzilla.gnome.org/show_bug.cgi?id=596262

js/ui/main.js

@@ -79,6 +79,15 @@ function start() {
         // Make sure not more than one run dialog is shown.
         getRunDialog().open();
     });
+    let shellwm = global.window_manager;
+    shellwm.takeover_keybinding("panel_main_menu");
+    shellwm.connect("keybinding::panel_main_menu", function () {
+        overview.toggle();
+    });
+    shellwm.takeover_keybinding("panel_run_dialog");
+    shellwm.connect("keybinding::panel_run_dialog", function () {
+       getRunDialog().open();
+    });
 
     overview = new Overview.Overview();
     chrome = new Chrome.Chrome();