send-email: test --no-thread --in-reply-to combination

3e0c4ff (send-email: respect in-reply-to regardless of threading,
2009-03-01) fixed the handling of the In-Reply-To header when both
--no-thread and --in-reply-to are in effect.  Add a test for it.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9001-send-email.sh

@@ -292,4 +292,15 @@ test_expect_success '--compose adds MIME for utf8 subject' '
 	grep "^Subject: =?utf-8?q?utf8-s=C3=BCbj=C3=ABct?=" msgtxt1
 '
 
+test_expect_success 'in-reply-to but no threading' '
+	git send-email \
+		--dry-run \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--in-reply-to="<in-reply-id@example.com>" \
+		--no-thread \
+		$patches |
+	grep "In-Reply-To: <in-reply-id@example.com>"
+'
+
 test_done