Previously, this directory was only preserved for failing tests. But
it's important to be able to easily debug known-broken tests, so
preserve the actual vs. expected output for those as well.
Git-style tests (test_expect_success etc.) suppress stdout and stderr
unless -v is given. Notmuch-style tests (created by test_begin_subtest
and test_expect_equal) do not have this behavior so implement it the
same.
Additionally, for both test styles, the test-lib.sh is changed so that
the content of suppressed stdout and stderr is shown in case of failed
test.
Finally a test for this functionality is added to basic tests.
Rather than *reall* sending mail here, we instead have a new test
program, smtp-dummy which implements (a small piece of) the
server-side SMTP protocol and saves a mail message to the filename
provided. This gives us reasonable test coverage of a large chunk of
the notmuch+emacs code base (down to talking to an SMTP server with
the final mail contents).
Since we are now using an explicit list of tests to run in
notmuch-test we need to be careful that we don't add a new file of
tests and then forget to add it to the list.
The numbers were meaningless, and they made it hard to find a file of interest.
Instead, we get the ordering we want by adding an explicit list of
tests to run to the notmuch-test script.
