The optimization idea removed here doesn't make sense anymore with
full-text indexing happening up front.
-Add back full-text indexing, (see last version of
-notmuch-index-message.c in the archives).
-
-Investigate using just a simple hash while constructing threads during
-"notmuch setup", then just writing out to Xapian in one shot at the
-end without haivng to rewrite documents nor look anything up.
-
Rename notmuch_thread_results_t and notmuch_message_results_t to
notmuch_threads_t and notmuch_messages_t respectively.