fix for 2794 : Delete are sometimes not replayed when they immediately follow a moddn
 
 When a delete is done on the new name of an entry immediately after renaming it,
the dependencies between these 2 operations are not detected and the delete
can therefore be replayed without waiting for the moddn to complete.
This cause the delete to fail and not being replayed.

These changes fix the dependency code and add a unit test case allowing
to reproduce the problem.