sql/log.cc:
  post-review fixes:
  * split log_type to log_state and log_type
  * rename log_type to log_table_type where appropriate (to avoid confusion)
  * merge MYSQL_SLOW_LOG and MYSQL_GENERAL_LOG to MYSQL_QUERY_LOG
sql/log.h:
  post-review fixes:
  * move last_time and reopen_file() to MYSQL_QUERY_LOG from the base class