Provide an option to make thread summaries keep initial subject

[Olivier Berger]

Hi.

Whenever a participant changes the subject in the middle of a thread,
the summary reported by notmuch search will change.

However, the result is that some mails tend to "disappear" from search
results, when (bad) participants reply instead of composing a new mail,
and change a subject (see
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=688699 for more details
on that problem, and a discussion). Of course, they're still there, but
their subject being masked, one may then grep or C-s for a particular
subject and miss them.

I think it would be interesting to allow notmuch to potentially keep the
original subject and not the most recent one for the thread summaries.

What do you think ?

Best regards,
-- 
Olivier BERGER 
http://www-public.it-sudparis.eu/~berger_o/ - OpenPGP-Id: 2048R/5819D7E8
Ingenieur Recherche - Dept INF
Institut Mines-Telecom, Telecom SudParis, Evry (France)