Merge branch 'ag/send-email-edit-threading-fix' into next

"git send-email" incremented its internal message counter when a
message was edited, which made logic that treats the first message
specially misbehave, which has been corrected.

* ag/send-email-edit-threading-fix:
  send-email: show the new message id assigned by outlook in the logs
  send-email: fix bug resulting in broken threads if a message is edited