test: Add new tests for out-of-order messages.

test: Add new tests for out-of-order messages.

These new tests demonstrate a bug as follows:

  Multiple messages are added to the database

  All of these message references a common parent

  The parent message does not exist in the databas

In this scenario, the messages will not be recognized as belonging to
the same thread. We consider this a bug, and the new tests treat this
as a failure.

Edited by Carl Worth <cworth@cworth.org>: Split these tests into their
own commit (before the fix of the bug). This lets me see the actual
failure in the test suite, before the fix is applied. Also fix the
alignment of new messages from test suite, (so that the PASS portions
all line up---which is important while we're still manually verifying
test-suite results).