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- Add support for Python 3.
- Eliminate ZODB dependency. Instead of raising a
``ZODB.POSException.StorageError`` for unexpected ``TypeErrors``
during commit, the new class
``nti.transactions.interfaces.CommitFailedError`` is raised.
- Introduce a new subclass of ``TransactionError``,
``AbortFailedError`` that is raised when an abort fails due to a
system error.