Issue 10470:  'python -m unittest' launches test discovery by default.(If you need to pass options to test discovery the discover subcommand must still be specified explicitly.)

The tests that were failing on (some) windows machines, where the
msg_XX.txt files used native \r\n lineseps are now also run on machines
that use \n natively, and conversely the \n tests are run on Windows.
The failing tests revealed one place where linesep needed to be added
to a flatten call in generator.  There was also another that the tests
didn't catch, so I added a test for that case as well.

Patch by Michele Orrù.

Patch by Rodolpho Eckhardt.

Schemenauer.