Re-applying the work initially done by Brian, and since worked upon by me previously in several separate patches to the 5.1 parent but never pushed.
WL#2952 - add simple single-table only transactions to federated.


sql/ha_federated.cc:
  added handlerton functions for commit and rollback, added handler methods for same.
sql/ha_federated.h:
  added member variable for transaction data (linked list of federated handlers used in transaction) and member functions for support commit and rollback.
mysql-test/r/federated_transactions.result:
  New BitKeeper file ``mysql-test/r/federated_transactions.result''
mysql-test/t/federated_transactions.test:
  New BitKeeper file ``mysql-test/t/federated_transactions.test''