Nti.transactions

==================

- When the ``TransactionLoop`` raises a ``CommitFailedError`` from a
``TypeError``, it preserves the original message.

- Test support for Python 3.6.

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- Add a new ObjectDataManager that will attempt to execute after
other ObjectDataManagers.

==================

- 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.