Merge branch 'tr/maint-1.6.0-send-email-irt'

* tr/maint-1.6.0-send-email-irt:
  send-email: test --no-thread --in-reply-to combination
  send-email: respect in-reply-to regardless of threading

Conflicts:
	t/t9001-send-email.sh

git-send-email.perl

@@ -821,7 +821,7 @@ Date: $date
 Message-Id: $message_id
 X-Mailer: git-send-email $gitversion
 ";
-	if ($thread && $reply_to) {
+	if ($reply_to) {
 
 		$header .= "In-Reply-To: $reply_to\n";
 		$header .= "References: $references\n";

t/t9001-send-email.sh

@@ -531,4 +531,15 @@ test_expect_success 'feed two files' '
 	test "z$(sed -n -e 2p subjects)" = "zSubject: [PATCH 2/2] add master"
 '
 
+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