fixed missing return for keybinding

.gitignore

@@ -11,3 +11,4 b' build'
 *.egg-info
 *~
 *.bak
+*.ipynb

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

@@ -68,6 +68,7 b' var IPython = (function (IPython) {'
             if ((event.ctrlKey || event.metaKey) && event.keyCode==83) { 
                 IPython.save_widget.save_notebook();
                 event.preventDefault();
+                return false;
             } else if (event.which === 27) {
                 // Intercept escape at highest level to avoid closing 
                 // websocket connection with firefox