Don't delete referenced messages from the Exchange server

* Addresses #2287439 incompletely
* The most likely reason for a reply/forward to get stuck in the Outbox
  is that the referenced message has been deleted from the client, with
  the deletion occuring BEFORE the message gets sent (currently, the two
  are completely independent)
* This change causes deletes NOT to be sent to the server if the message
  to be deleted is referenced by an outgoing message

Change-Id: I146f63ab345c07e684790e1d7d1fc08870468bbf
3 files changed