This adds five tests for the five main cases in the fancy from guessing.
It assumes that you have applied
id:1271451102-11336-1-git-send-email-hohndel@infradead.org which will get you
the latest fancy From guessing.

We have one test case each for
- nothing to go on
- Envelope-To:
- X-Original-To:
- Received: ... for ...
- Received: domain guessing

The second patch adds the Bcc headers that you will get as part of the 
results with an unpatched notmuch. I consider these Bcc headers broken
as they are a potential information leak; the Bcc always goes to the
primary email address, so information that isn't related to that account
is still routed back to it. Bcc logic should be fixed to copy the address
that is used as From: address

But since I don't use Bcc at all I didn't attempt to fix that part.

/D