Track revision history of comments when edited?

If a commenter edits his comment after making it, or if an Editor edits the comment, is there a way to view the previous revision(s) of the comment before the edit was made?  This seems like an important feature for comment software to have, both for moderation purposes (i.e. a commenter is hiding his original message to someone by blanking it later) and for administrative purposes (i.e., making sure an Editor is using his editing powers wisely).