It's time to put full-text indexing back, and we might want to
experiment with optimization the original thread-stitching phase.
+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.