Change button labels in restart dialog to action words.

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

@@ -735,11 +735,11 b' var IPython = (function (IPython) {'
             modal: true,
             title: "Dead kernel",
             buttons : {
-                "Yes": function () {
+                "Restart": function () {
                     that.start_kernel();
                     $(this).dialog('close');
                 },
-                "No": function () {
+                "Continue running": function () {
                     $(this).dialog('close');
                 }
             }