Now, every transaction (including autocommit transactions) starts with
a BEGIN and ends with a COMMIT/ROLLBACK in the binlog.
Added a test case, and updated lots of test case result files.


mysql-test/r/multi_update.result:
  Updated result file
mysql-test/r/sp_trans_log.result:
  Updated result file
mysql-test/suite/binlog/r/binlog_innodb.result:
  Updated result file
mysql-test/suite/binlog/r/binlog_multi_engine.result:
  Updated result file
mysql-test/suite/binlog/r/binlog_stm_blackhole.result:
  Updated result file
mysql-test/suite/binlog/r/binlog_stm_mix_innodb_myisam.result:
  Updated result file
mysql-test/suite/ndb/r/ndb_binlog_format.result:
  Updated result file
mysql-test/suite/rpl/r/rpl_innodb_mixed_dml.result:
  Updated result file
mysql-test/suite/rpl/r/rpl_row_charset_innodb.result:
  Updated result file
mysql-test/suite/rpl/r/rpl_row_create_table.result:
  Updated result file
mysql-test/suite/rpl/r/rpl_row_log_innodb.result:
  Updated result file
mysql-test/suite/rpl/r/rpl_switch_stm_row_mixed.result:
  Updated result file
mysql-test/suite/rpl/r/rpl_truncate_3innodb.result:
  Updated result file
mysql-test/suite/rpl/t/rpl_row_create_table.test:
  Updated result file
mysql-test/suite/rpl_ndb/r/rpl_ndb_stm_innodb.result:
  Updated result file
sql/log.cc:
   - Always write BEGIN and COMMIT around statements, even in autocommit
     mode.
   - Added comments for binlog_commit and binlog_rollback.
sql/log_event.cc:
  Added debug trigger to avoid writing xid events to the binlog.
mysql-test/suite/rpl_ndb/r/rpl_ndb_transaction.result:
  Results for new test case
mysql-test/suite/rpl_ndb/t/rpl_ndb_transaction-master.opt:
  Options for new test case
mysql-test/suite/rpl_ndb/t/rpl_ndb_transaction-slave.opt:
  Options for new test case
mysql-test/suite/rpl_ndb/t/rpl_ndb_transaction.test:
  Added new test case.