The test uses the 'z' option, i.e. "compress the output while at
it", which is GNUism and not portable.
Reported-by: Armin Kunaschik <megabreit@googlemail.com> Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>