Reduce repeated code regarding restarting events

IPython/frontend/html/notebook/static/js/notificationwidget.js

@@ -65,8 +65,7 b' var IPython = (function (IPython) {'
                 title: "Dead kernel",
                 buttons : {
                     "Restart": function () {
-                        IPython.save_widget.update_document_title();
-                        that.set_message("Restarting kernel",500);
+                        $([IPython.events]).trigger('status_restarting.Kernel');
                         IPython.notebook.start_kernel();
                         $(this).dialog('close');
                     },