Added slow_query_log & general_log global upadatable variables.
Added slow-query-log & general-log startup options.
Added log_output, general_log_file, slow_query_log_file global updatable variables.


mysql-test/r/show_check.result:
  WL#3015: Logging Improvements - No Restarts
  result fix
sql/log.cc:
  WL#3015: Logging Improvements - No Restarts
  added methods to LOGGER class
  void deactivate_log_handlers(THD* thd, uint log_type);
  bool activate_log_handlers(THD* thd, uint log_type);
  added methods to Log_to_file_event_handler:
  TABLE_LIST *get_mysql_slow_log()
  TABLE_LIST *get_mysql_log()
sql/log.h:
  WL#3015: Logging Improvements - No Restarts
  added methods to LOGGER class
  void deactivate_log_handlers(THD* thd, uint log_type);
  bool activate_log_handlers(THD* thd, uint log_type);
  added methods to Log_to_file_event_handler:
  TABLE_LIST *get_mysql_slow_log()
  TABLE_LIST *get_mysql_log()
sql/mysql_priv.h:
  WL#3015: Logging Improvements - No Restarts
sql/mysqld.cc:
  WL#3015: Logging Improvements - No Restarts
  added 'slow-query-log' & 'general-log' options
sql/set_var.cc:
  WL#3015: Logging Improvements - No Restarts
  added 'slow_query_log' & 'general_log' updatable variables
  added 'log_output', 'general_log_file', 'slow_query_log_file' updatable variables
sql/set_var.h:
  WL#3015: Logging Improvements - No Restarts
  new class sys_var_log_state
  new class sys_var_log_output
sql/share/errmsg.txt:
  WL#3015: Logging Improvements - No Restarts
  added error message
sql/sql_delete.cc:
  WL#3015: Logging Improvements - No Restarts
  'truncate table slow_log|general', keep status of logs