send-email: 'References:' should only reference what is sent

If someone responded with a negative (n|no) to the confirmation,
then the Message-ID of the discarded email is no longer used
in the References: header of subsequent emails.

Consequently, send_message() now returns 1 if the message was
sent and 0 otherwise.

Signed-off-by: Michael Witten <mfwitten@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -796,6 +796,10 @@ sub sanitize_address
 
 }
 
+# Returns 1 if the message was sent, and 0 otherwise.
+# In actuality, the whole program dies when a there
+# is an error sending a message.
+
 sub send_message
 {
 	my @recipients = unique_email_list(@to);
@@ -864,7 +868,7 @@ X-Mailer: git-send-email $gitversion
 		         default => $ask_default);
 		die "Send this email reply required" unless defined $_;
 		if (/^n/i) {
-			return;
+			return 0;
 		} elsif (/^q/i) {
 			cleanup_compose_files();
 			exit(0);
@@ -945,7 +949,7 @@ X-Mailer: git-send-email $gitversion
 		$smtp->data or die $smtp->message;
 		$smtp->datasend("$header\n$message") or die $smtp->message;
 		$smtp->dataend() or die $smtp->message;
-		$smtp->ok or die "Failed to send $subject\n".$smtp->message;
+		$smtp->code =~ /250|200/ or die "Failed to send $subject\n".$smtp->message;
 	}
 	if ($quiet) {
 		printf (($dry_run ? "Dry-" : "")."Sent %s\n", $subject);
@@ -966,6 +970,8 @@ X-Mailer: git-send-email $gitversion
 			print "Result: OK\n";
 		}
 	}
+
+	return 1;
 }
 
 $reply_to = $initial_reply_to;
@@ -1126,10 +1132,10 @@ foreach my $t (@files) {
 
 	@cc = (@initial_cc, @cc);
 
-	send_message();
+	my $message_was_sent = send_message();
 
 	# set up for the next message
-	if ($chain_reply_to || !defined $reply_to || length($reply_to) == 0) {
+	if ($message_was_sent and $chain_reply_to || not defined $reply_to || length($reply_to) == 0) {
 		$reply_to = $message_id;
 		if (length $references > 0) {
 			$references .= "\n $message_id";