don't set LOG_EVENT_BINLOG_IN_USE_F for relay logs
sql/sql_repl.cc
    clear LOG_EVENT_BINLOG_IN_USE_F flag before sending an event to a slave


sql/log.cc:
  don't set LOG_EVENT_BINLOG_IN_USE_F for relay logs
sql/sql_repl.cc:
  clear LOG_EVENT_BINLOG_IN_USE_F flag before sending an event to a slave