"Federated Denial of Service"
  Federated storage engine used to attempt to open connections within
  the ::create() and ::open() methods which are invoked while LOCK_open
  mutex is being held by mysqld. As a result, no other client sessions
  can open tables while Federated is attempting to open a connection.
  Long DNS lookup times would stall mysqld's operation and a rogue
  connection string which connects to a remote server which simply
  stalls during handshake can stall mysqld for a much longer period of
  time.
  This patch moves the opening of the connection much later, when the
  federated actually issues queries, by which time the LOCK_open mutex is
  no longer being held.


mysql-test/r/federated.result:
  change of test/results due to patch for bug25679
mysql-test/t/federated.test:
  change of test/results due to patch for bug25679
sql/ha_federated.cc:
  bug25679
    remove function check_foreign_fata_source()
    ha_federated::open() no longer opens the federated connection.
    ha_federated::create() no longer opens and tests connection.
    ha_federated::real_connect() opens connection and tests presence of table.
    ha_federated::real_query() sends query, calling real_connect() if neccessary.
sql/ha_federated.h:
  bug25679
    new methods real_query() and real_connect()