pipe: Use Delivered-To and Message-Id from outer

If a wrapped mail is sent, copy the Delivered-To header into the nested
message so it will be clear(er) how the mail arrived into the system. Also,
copy the Message-Id into the nested mail if there is none to help against
mails delivered repeatedly.
Merge pull request #528 from greezybacon/issue/wrapped-mid-delivered-to

pipe: Use Delivered-To and Message-Id from outer

Reviewed-By: Peter Rotich <peter@osticket.com>