AUTH_ldap lookupUers needs to close the ldap connection

[Bill Gosse]

AUTH_ldap class's lookupUers function should close the lpad connection once its done authenticating/binding the user.

        if (!@ldap_bind($connect, $username, $password)) {
            ldap_close($connect);
            return false; // if we can't bind it's likely the user is unknown or the password is wrong
        }
        $this->log('Bound');

        ldap_close($connect);
        return true;