Failing Test (since commit 53a5a48aed7d87aa1533c0bcbd72e41b686527d8)

Hi,

It seems to be a regression since the commit https://github.com/doctrine/doctrine2/commit/53a5a48aed7d87aa1533c0bcbd72e41b686527d8

Doctrine\ORM\PersistentCollection can be populated in $changeSet if you set a PreUpdate and PostUpdate event.

Original issue: http://www.doctrine-project.org/jira/browse/DDC-3033
Update DDC3033Test.php
Update DDC3033Test.php
[DDC-3033] Fix bug in UnitOfWork#recomputeSingleEntityChangeSet.

The fix for DDC-2624 had a side effect on recomputation of
changesets in preUpdate events. The method wasn't adjusted
to the changes in its sister method computeChangeSet() and
had wrong assumptions about the computation.

Especially:
1. Collections have to be skipped
2. Comparison was changed to strict equality only.
[DDC-3033] Clarify restrictions in events.
Merge branch 'DDC-3033'