Allow replying to trac emails to update ticket

[Simon Fondrie-Teitler]

Currently:

[ text/plain ]
This is the mail system at host mx1.riseup.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

		   The mail system

<trac@mediagoblin.org>: host mail.mediagoblin.org[66.228.56.33] said: 550 5.1.1
    <trac@mediagoblin.org>: Recipient address rejected: User unknown in local
    recipient table (in reply to RCPT TO command)
[ message/delivery-status ]
Reporting-MTA: dns; mx1.riseup.net
X-Postfix-Queue-ID: 5449F464B5
X-Postfix-Sender: rfc822; simonft@riseup.net
Arrival-Date: Sat, 13 Jul 2013 02:45:02 -0700 (PDT)

Final-Recipient: rfc822; trac@mediagoblin.org
Original-Recipient: rfc822;trac@mediagoblin.org
Action: failed
Status: 5.1.1
Remote-MTA: dns; mail.mediagoblin.org
Diagnostic-Code: smtp; 550 5.1.1 <trac@mediagoblin.org>: Recipient address
    rejected: User unknown in local recipient table

[Simon Fondrie-Teitler]

This would work, but is a little difficult to set up.

​https://oss.trac.surfsara.nl/email2trac