re-using unused LOCK_active_mi to serialize all administrative
commands related to replication:
START SLAVE, STOP SLAVE, RESET SLAVE, CHANGE MASTER, init_slave()
(replication autostart at server startup), end_slave() (replication
autostop at server shutdown), LOAD DATA FROM MASTER.
This protects us against a handful of deadlocks (like BUG#2921
when two START SLAVE, but when two STOP SLAVE too).
Removing unused variables.


sql/item_func.cc:
  We don't need LOCK_active_mi just to MASTER_POS_WAIT().
sql/repl_failsafe.cc:
  no need for macro
sql/set_var.cc:
  no need for macro
sql/slave.cc:
  Re-using unused LOCK_active_mi to serialize all administrative
  commands related to replication:
  START SLAVE, STOP SLAVE, RESET SLAVE, CHANGE MASTER, init_slave()
  (replication autostart at server startup), end_slave() (replication
  autostop at server shutdown), LOAD DATA FROM MASTER.
  This protects us against a handful of deadlocks.
  Removing unused variables.
sql/slave.h:
  Re-using LOCK_active_mi to serialize administrative replication commands.
  Macros unneeded. Removing unneeded variables.
sql/sql_parse.cc:
  found unused variable.
  Replacing macros.
sql/sql_show.cc:
  replacing macros