Merge branch from fixing up bugs after bisecting.

Merge branch from fixing up bugs after bisecting.

I'm glad that when I implemented "notmuch restore" I went through the
extra effort to take the code I had written in one sitting into over a
dozen commits. Sure enough, I hadn't tested well enough and had
totally broken "notmuch setup", (segfaults and bogus thread_id
values).

With the little commits I had made, git bisect saved the day, and I
went back to make the fixes right on top of the commits that
introduced the bugs. So now we octopus merge those in.