Code review comment for lp:~jaypipes/drizzle/explicit-transaction

    Completes the work of removing the weirdness around transaction
    boundaries in the storage engine API.

    * Transactional storage engines are now all explicitly notified
      of the start of a new "normal" transaction in the new PSE API
      method plugin::TransactionalStorageEngine::doStartTransaction()
      This new method takes a start_transaction_option_t as one of its
      parameters, and passing this option allows the storage engine
      API to cleanly signal the start of a consistent snapshot (and in
      the future additional transaction attributes). This meant the
      removal of the old start_consistent_snapshot() method.

    * The TransactionServices component now fully manages the transaction
      boundaries, notification of transaction boundaries to participating
      resource managers (transactional storage engines)

    Adds a simple test case (to be expanded with future XA work) for
    transaction behaviour.