git-send-email.perl: Add angle brackets to In-Reply-To if necessary

Although message-id by defintion should have surrounding angle
brackets, there is no point forcing people to type them in.

Signed-off-by: David Kastrup <dak@gnu.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -317,7 +317,8 @@ sub expand_aliases {
 	} while (!defined $_);
 
 	$initial_reply_to = $_;
-	$initial_reply_to =~ s/(^\s+|\s+$)//g;
+	$initial_reply_to =~ s/^\s+<?/</;
+	$initial_reply_to =~ s/>?\s+$/>/;
 }
 
 if (!$smtp_server) {