Sending headers

Add headers to stop auto-responders from replying

    Precedence: bulk
    Auto-Submitted: auto-generated

are the headers we're adding.  This should mean that vacation auto
responders don't bother sending a reply to us.

Background reading at http://stackoverflow.com/a/301958/3189

(btw to avoid seeing the whitespace changes, add `?w=1` to the URL)