typo, use keycodes object instead of magic numbers

IPython/html/static/notebook/js/cell.js

@@ -238,7 +238,7 var IPython = (function (IPython) {
      * @param {event} event -
      * @return {Boolean} `true` if CodeMirror should ignore the event, `false` Otherwise
      */
-    CodeCell.prototype.handle_keyevent = function (editor, event) {
+    Cell.prototype.handle_keyevent = function (editor, event) {
 
         // console.log('CM', this.mode, event.which, event.type)
 

IPython/html/static/notebook/js/codecell.js

@@ -197,7 +197,7 var IPython = (function (IPython) {
         if (event.keyCode === keycodes.enter && (event.shiftKey || event.ctrlKey || event.altKey)) {
             // Always ignore shift-enter in CodeMirror as we handle it.
             return true;
-        } else if (event.which === 40 && event.type === 'keypress' && IPython.tooltip.time_before_tooltip >= 0) {
+        } else if (event.which === keycodes.down && event.type === 'keypress' && IPython.tooltip.time_before_tooltip >= 0) {
             // triger on keypress (!) otherwise inconsistent event.which depending on plateform
             // browser and keyboard layout !
             // Pressing '(' , request tooltip, don't forget to reappend it