[WIP] fix NestedTree after upgrade to doctrine v2.4.3

I have found the cause why we have problems. Only one line in UOW https://github.com/doctrine/doctrine2/blob/v2.4.3/lib/Doctrine/ORM/UnitOfWork.php#L933

This hot fix works for my NestedTree entities. I think that can work for the other extensions by analogy.