t7502: use diff.noprefix for --verbose test

To check that "status -v" respects diff config, we set
"color.diff" and look at the output of "status". We could
equally well use any diff config. Since color output depends
on a lot of other factors (like whether stdout is a tty, and
how we interpret "always"), let's use a more mundane option.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7502-commit.sh

@@ -171,9 +171,9 @@ test_expect_success 'verbose' '
 
 test_expect_success 'verbose respects diff config' '
 
-	test_config color.diff always &&
+	test_config diff.noprefix true &&
 	git status -v >actual &&
-	grep "\[1mdiff --git" actual
+	grep "diff --git negative negative" actual
 '
 
 mesg_with_comment_and_newlines='