The tests for the comment dialog were failing in Firefox due to a missed

spy. The problem is that the text editor was calling .focus() on the

jQuery-wrapped element when using plain text editors, but the spy was

looking for the element itself.
This change updates the TextAreaWrapper to call .el.focus() instead

of .$el.focus(). This makes things consistent between plain text areas

and codemirror versions, so the spy works in both cases.

Ran unit tests.