Documented/cleaned up log event code
Updated tests


mysql-test/r/rpl000014.result:
  new binlog format
mysql-test/r/rpl000015.result:
  new binlog format
mysql-test/r/rpl000016.result:
  new binlog format
mysql-test/std_data/master-bin.001:
  new binlog format
mysql-test/t/rpl000014.test:
  new binlog format
sql/log.cc:
  new binlog format
sql/log_event.cc:
  new binlog format
sql/log_event.h:
  new binlog format
sql/sql_class.cc:
  new binlog format
sql/sql_class.h:
  new binlog format
sql/sql_repl.cc:
  new binlog format