- Fix that binlog_gtid_pos() (and hence slave connect) does not work
   correctly in the very first binlog file (due to not logging empty
   Gtid_list_log_event).

 - Remove one instance of the stupid domain_id-0-is-implicit.

 - Rename the confusing Gtid_Pos_Auto in SHOW SLAVE STATUS to Using_Gtid.

 - Fix memory leak.