Optimize calls to current_thd


mysql-test/r/mix_innodb_myisam_binlog.result:
  updated results
mysql-test/t/mix_innodb_myisam_binlog.test:
  Fix for 4.1
sql/ha_innodb.cc:
  Don't call current_thd in an assert that is not deleted in release version
  (Because current_thd is slow)