instrumented the server with DBUG_SYNC_POINT() macro


mysql-test/t/rpl_log.test:
  no change
sql/item_func.cc:
  debug_sync_point()
sql/log_event.cc:
  clead load data file tmpdir on slave on start/stop events
sql/mysql_priv.h:
  DBUG_SYNC_POINT
sql/sql_repl.cc:
  DBUG_SYNC_POINT in Create_file_event