* (bug 2740) Accept image deletions on 'enter' submit from MSIE

* (bug 2740) Accept image deletions on 'enter' submit from MSIE
Confirmation checkbox is gone now; the submit button had been
coopted to replace it in the submission variables, but some
user agents don't go looking for a default button when you
submit by hitting 'enter' in a text entry widget. Just check
that the form was posted; we already have the edit token check
to confirm that it's not a forged request.