test-lib: Replace uses of $(expr ...) by POSIX shell features.

diff --git a/git-send-email.perl b/git-send-email.perl
index 57127aa823833f75fb546e738fcb19381fc331f7..546d2ebc0c72d4a330b3b40ca886af9340afb5af 100755 (executable)
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -821,7 +821,7 @@ sub send_message
 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";