Users cannot undo their votes on questions or replies

Once a user casts a vote, the voting of the question/reply is closed for that user. In stackoverflow a user can undo his vote by casting a vote opposite to the original one, I expected the same behavior with EasyDiscuss.

Please provide an updated version of the votes/view.ajax.php file or post a code snippet with the logic to check if the user is trying to cast the same vote type more than one time.

Thanks