Session key regex is too restrictive

I ran into this issue while trying to deserialize a PHP session that included keys with dots (Devise uses `warden.user.user.key` by default to store the current user id for authentication). From the PHP docs on session.serialize_handler (http://www.php.net/manual/en/session.configuration.php#ini.session.serialize-handler) it looks as if any character except | (pipe) and ! is valid.