After-fix optimizations proposed and finally
implemented by Monty.


mysql-test/r/lock.result:
  BUG#5390 - problems with merge tables
  After-fix optimizations proposed and finally
  implemented by Monty.
  Additional test results.
mysql-test/t/lock.test:
  BUG#5390 - problems with merge tables
  After-fix optimizations proposed and finally
  implemented by Monty.
  Additional tests.
sql/lock.cc:
  BUG#5390 - problems with merge tables
  After-fix optimizations proposed and finally
  implemented by Monty.
  get_lock_data() gets a flag for storing the lock
  positions in the new TABLE elements.
  mysql_lock_remove() can now remove a lock faster
  and more precisely as it has needed info in TABLE now.
  mysql_unlock_read_tables() and mysql_lock_merge() must 
  now adjust the new elements of TABLE when modifying locks.
  mysql_lock_have_duplicate() can now work faster on
  the existing lock as the positions in the lock
  arrays are known for each table.
  get_lock_data() assigns the new TABLE elements 
  on request of the new flag.
sql/table.h:
  BUG#5390 - problems with merge tables
  After-fix optimizations proposed and finally
  implemented by Monty.
  Additional elements of TABLE.