#23 Add a pref for nixing referrer URLs

[Dan A Thompson]

It would be nice if there were an option to do whatever
magic is required to nix referrer URLs, if possible.

For example, take this URL:
http://db.gamefaqs.com/console/ps2/file/sly_cooper_sprint.txt

When this shows up in an IlohaMail message (with
target="_blank"), I can go straight to it. But going
to it from bEasy triggers their deep-link detector.