[feature request] notmuch_thread_get_newest_subject

[Patrick Totzke]

Hi all,

There seems to be no way to get the "current" subject line of a thread.
I promised to relay my feature request to the list, so here it is..

This could be done using a parameter like "newest-or-original" for 
`notmuch_thread_get_subject` in threads.cc,
which would look up the newest message in the thread and return its subject.

Secondly, this should be usable from the python bindings.
I intend to use this in alot to display the newest subject for a thread by default.

cheers,
/p