Fixing Shift-Enter bug in text cells.

Hitting Shift-Enter on an already rendered text cell should simply
move past it. It was causing the cell to enter edit mode. This
is not fixed.

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

@@ -49,7 +49,7 var IPython = (function (IPython) {
         IPython.Cell.prototype.bind_events.apply(this);
         var that = this;
         this.element.keydown(function (event) {
-            if (event.which === 13) {
+            if (event.which === 13 && !event.shiftKey) {
                 if (that.rendered) {
                     that.edit();
                     return false;