revert: free msg in format_todo()

Memory allocated to the fields of msg by get_message() isn't freed.
This is potentially a big leak, because fresh memory is allocated to
store the commit message for each commit.  Fix this using
free_message().

Reported-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/revert.c

@@ -709,6 +709,7 @@ static int format_todo(struct strbuf *buf, struct commit_list *todo_list,
 		if (get_message(cur->item, &msg))
 			return error(_("Cannot get commit message for %s"), sha1_abbrev);
 		strbuf_addf(buf, "%s %s %s\n", action_str, sha1_abbrev, msg.subject);
+		free_message(&msg);
 	}
 	return 0;
 }