Monty revoked any locks for temporary tables in
ha_myisam::external_lock()
But further code bans using write cache on nonlocked tables
this makes operations much slower


myisam/mi_locking.c:
  Handling of MI_TEMPORARY_TABLE lock
myisam/myisamdef.h:
  defining of MI_TEMPORARY_TABLE
sql/ha_myisam.cc:
  now we lock temporary tables using MI_TEMPORARY_TABLE lock