v1: fix for threading of replies to ghost messages

[David Bremner]

Gregor Zattler <telegraph at gmx.net> writes:

>
> I applied the patches and looked with notmuch-emacs for threads
> which before would probably show wrong ordering of messages.  The
> half a dozen threads were all shown in the correct order with
> respect to parents and children, but I found from those not
> disclosable RT ticket mails (I mentioned in above referenced
> thread):

Can you also try the series at

    id:20180723082259.32440-1-david at tethera.net?

I'm not sure if it's related, but it does fix replies for a different
bug tracker. You will have to reindex the messages in question
(e.g. using notmuch reindex).