[PATCH 00/11] Fix search tagging races

[Austin Clements]

I was hacking on undo support for notmuch-emacs and sort of
accidentally wrote this instead.  This series fixes a set of
well-known races where tagging from search-mode unexpectedly affects
messages that arrived after the search was performed (and hence the
user doesn't know they're tagging them).  We've attacked this a few
times before, but have always run up against something that was
missing.  It turns out the pieces are finally all in place.

The first five patches just clean various things up in preparation.
Patches 6 and 7 add support for tagging large queries, which would
otherwise become a problem when later patches start using explicit
message ID-based queries for tagging.  The remaining four patches
actually fix the search tagging races using explicit message ID-based
queries.

It's a fairly long series, but none of the patches are very big.