"Federated INSERT failures"
  Federated does not correctly handle "INSERT...ON DUPLICATE KEY UPDATE"
  However, implementing such support is not reasonably possible without
  increasing complexity of the storage engine: checking that constraints
  on remote server match local server and parsing error messages.
  This patch causes 'ON DUPLICATE KEY' to fail with ER_DUP_KEY message
  if a conflict occurs and not to fail silently.