t7508: demonstrate status's failure to use --porcelain format with -z

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>

t/t7508-status.sh

@@ -364,6 +364,13 @@ test_expect_success 'status submodule summary (clean submodule)' '
 	test_cmp expect output
 '
 
+test_expect_failure 'status -z implies porcelain' '
+	git status --porcelain |
+	perl -pe "s/\012/\000/g" >expect &&
+	git status -z >output &&
+	test_cmp expect output
+'
+
 cat >expect <<EOF
 # On branch master
 # Changes to be committed: