protect prepare-...-commit with a mutex to ensure that commits in binlog and in the innodb have the same order
    store binlog position with the commit


innobase/include/trx0trx.h:
  comment modified
sql/ha_innodb.cc:
  protect prepare-...-commit with a mutex to ensure that commits in binlog and in the innodb have the same order
  store binlog position with the commit
sql/handler.cc:
  ha_prepare cannot return -1