Goto line 291, add condition as below:
if ((($post->userid <> $USER->id) and !$adminedit) and (($post->userid <> $USER->id) and !teachersuperedit)) {
Goto line 294, add condition as below:
if ((((time() - $post->created) > $CFG->maxeditingtime) and !$adminedit) and (((time() - $post->created) > $CFG->maxeditingtime) and !$teachersuperedit)) {
--
Anyway, I should think about that
Let it be a prebeta solution