Fix typo in Kolab passwd driver

Patch by Mike Gabriel, originally reported at https://bugs.debian.org/780670

Signed-off-by: Michael J Rubinsky <mrubinsk@horde.org>

passwd/lib/Driver/Kolab.php

@@ -73,7 +73,7 @@ protected function _changePassword($user, $oldpass, $newpass)
         $userdn = ldap_get_dn($ds, $entry);
 
         // Connect as the user.
-        $result = @ldap_bind($ds, $userdn, $old_password);
+        $result = @ldap_bind($ds, $userdn, $oldpass);
         if (!$result) {
             throw new Passwd_Exception(_("Incorrect old password."));
         }