Fellow hackers,

So, I have always wondered why Notmuch uses the strangest buffer titles
ever, and yesterday I decided to take a look under the hood...  I found
that the code in 'notmuch-search-buffer-title' defines and uses a pair
of variables, named 'longest' and 'longest-length', but never sets the
latter, which causes the strange buffer titles I observe.  Please see
the attached patch with a fix.

P.S. I could not make the test suite work, not in the time I had for the
fix, so ... see the test in the commit message. :)

Rudy