I still don't know everything about how I want search order to be
customizable, but I do like the current defaults, (namely, performing
a new search gives results newest first, but performing a saved search
like "tag:inbox" gives results as oldest first).
Until we come up with a better plan for people to select what *they*
want, (rather than just getting what I want), let's codify the current
results in the test suite.
Some recently-added tests used hard-coded thread ID values in search
specifications. This is unreliable since the thread IDs depend on the
order in which "notmuch new" encounters new files, (which in turn can
depend on inode ordering within the filesystem).
Fix these by using the new "notmuch search --output=threads" to find the
correct thread IDs given a hard-coded (but reliable) message ID.
