Changes from DDC-1690 trigger a bug in entity merging

Following the changes for DDC-1690, I encountered a serious bug in how EntityManager::merge(...) functions for entities that use NOTIFY change tracking. It's related to interaction between lazy loading and calls to addPropertyChangedListener().

Scenario:

• EntityA has a One-To-One, lazy-load association to EntityB
• EntityB implements NotifyPropertyChanged and uses change tracking policy "NOTIFY"

Steps to reproduce:

1. $instanceA = $em->find('EntityA', $id)
2. $em->clear()
3. $instanceA = $em->merge($instanceA)
4. $instanceA->getB() will return a proxy for B that is marked as initialized by contains no data

Workaround: Mark EntityB::addPropertyChangedListener(...) as 'final', so it doesn't get proxied and lazy loading is not triggered.