Implements hook_comment_update().
The Comment module doesn't call hook_comment_unpublish() when saving individual comments, so we need to check for those here.
function forum_comment_update($comment) {
// comment_save() calls hook_comment_publish() for all published comments,
// so we need to handle all other values here.
if (!$comment->status) {
_forum_update_forum_index($comment->nid);
}
}