Partial fix for #3525: Attribute modifications are not replicated for modDN operations
Warning: ModifyDNMsg PDU is updated and modifications are exchanged through the replication network.
However at replay time, the moddn operation is re-created with the modifications, but they cannot be replayed at this time:
The comment of the addModification() method for ModifyDNOperation states that "This should only be called by pre-operation plugins"

So either some modifs are to be done on core side, or we may put the modifications in the operaton context and intercept the replay
at the pre-op stage and effectively replay the modifications at this time.

...to be discussed.