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


mysql-test/t/rpl_transaction-master.opt:
  BitKeeper file /home/sven/bk/b26395-autocommit-xa/5.0-rpl/mysql-test/t/rpl_transaction-master.opt
mysql-test/t/rpl_transaction-slave.opt:
  BitKeeper file /home/sven/bk/b26395-autocommit-xa/5.0-rpl/mysql-test/t/rpl_transaction-slave.opt
mysql-test/r/mix_innodb_myisam_binlog.result:
  Updated result file
mysql-test/r/multi_update.result:
  Updated result file
mysql-test/r/rpl_transaction.result:
  New result file for new test case.
mysql-test/r/sp_trans_log.result:
  Updated result file
mysql-test/r/variables-big.result:
  Updated result file
mysql-test/t/rpl_transaction.test:
  New test case.
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.