This note was described in the previous commit message, but mistakenly
not committed:
The note about making "notmuch setup" faster is now rewritten to apply
to "notmuch new" since "notmuch setup" no longer does any mail
indexing.
new directory will result in notmuch creating new timestamp documents
and leaving stale ones behind.)
+Ensure that "notmuch new" is sane if its first, giant indexing session
+gets interrupted, (that is, ensure that any results indexed so far are
+flushed).
+
Fix notmuch.c to use a DIR prefix for directory timestamps, (the idea
being that it can then add other non-directory timestamps such as for
noting how far back in the past mail has been indexed, and whether it