When 'git status' is supplied the -z switch, and no output format has been
selected, it is supposed to use the --porcelain format. This does not
happen. Instead, the standard long format is used. Add a test to
demonstrate this failure.
Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil> Signed-off-by: Junio C Hamano <gitster@pobox.com>