Cleaned up patch for checking locks for multi-table updates


myisam/mi_close.c:
  Reverted patch for new usage of open_counts
myisam/mi_locking.c:
  Reverted patch for new usage of open_counts
sql/ha_myisam.cc:
  Reverted patch for new usage of open_counts
sql/handler.cc:
  Removed compiler warning
sql/sql_acl.cc:
  Removed compiler warning
sql/sql_table.cc:
  No need to unlock after failed call to external_lock()
sql/sql_update.cc:
  Cleaned up (and made it more secure) patch for checking locks for multi-table updates