the fact that the transaction log is empty does not mean we're not in a transaction
(it could be BEGIN; SELECT * FOR UPDATE FROM ibtable: then we don't want to commit now, even if
the statement is a MyISAM update).
With a testcase.


mysql-test/r/mix_innodb_myisam_binlog.result:
  result update
mysql-test/t/mix_innodb_myisam_binlog.test:
  test update for a new bug
sql/log.cc:
  The fact that the transaction log is empty does not mean we're not in a transaction
  (it could be BEGIN; SELECT * FOR UPDATE: then we don't want to commit now).