Modifying CodeMirror focus hack to work better.

I had removed a text area focus event earlier today and that
broke the . key. We are still having problems with CodeMirror
elements gaining focus, but this seems to fix the issue.

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

@@ -184,7 +184,6 b' var IPython = (function (IPython) {'
         // While this seems to fix the issue, this should be fixed
         // in CodeMirror proper.
         var s = this.code_mirror.getValue();
-        if (s === '') this.code_mirror.setValue('.');
         this.code_mirror.focus();
         if (s === '') this.code_mirror.setValue('');
     };