[notmuch] Notmuch performance problems on OSX

[Oliver Charles]

I just upgraded to xapian-core HEAD and notmuch master tip today, in
desparation to get away from GMail. Sadly it's still taking at least
0.7s to tag a single thread (with one message). I'm really eager to
solve this, could anyone give me any pointers on how I could go about
profiling it or finding the cause of this problem?
-- 
    Oliver Charles / aCiD2