innobase/row/row0ins.c:
  If the SQL-query will update or replace duplicate key row we take X-lcok
  for duplicate row.
sql/ha_innodb.cc:
  INSERT ON DUPLICATE KEY UPDATE will also update duplicate key and we can
  take X-lock in this case for duplicate key records.
BitKeeper/etc/ignore:
  Added innobase/row/row0index.c to the ignore list