Transaction meta data cleanup

Convert to unicode if bytes are given.

  defined to be text (unicode) as apposed to Python the ``str`` type.

- Added the ``extended_info`` transaction attribute which contains
  transaction meta data.  (The ``_extension`` attribute is retained as
  an alias for backward compatibility.)

  The transaction interface, ``ITransaction``, now requires
  ``extended_info`` keys to be text (unicode) and values to be
  JSON-serializable.

Run decorator, a simpler alternative to attempts

Fix #19 attempts didn't stop on success

It's nice if docs are tested, but doctests shouldn't pollute docs.

Uses fix from https://github.com/zopefoundation/transaction/pull/20/files
but different test changes.

Should fix build failures on slightly-older setuptools installations,
e.g.: http://jenkins.pylonsproject.org/job/transaction/53/console.

Update URL in setup.py Thanks!

Corrected ITransaction: removed beforeCommitHook and 2 misplaced 'self' parameters

Corrected ITransaction: removed beforeCommitHook (no longer implemented) and two misplaced 'self' args.

Restore display of missing lines.

Add new testing dep, 'mock' for coverage env.

Coverage 4.1 defaults 'show_missing' to False.

Notify data managers that join transactions in progress

  transactions were in progress didn't have their newTransaction
  methods called to let them know of the in-progress transactions.

New transaction API for storing data on behalf of objects

And that it's id is used.

For objects such as data managers or their subobjects that
work with multiple transactions, it's convenient to store
transaction-specific data on the transaction itself.  The
transaction knows nothing about the data, but simply holds it
on behalf of the object.

Discussion:
https://groups.google.com/forum/#!topic/python-transaction/oUzj3uIHBgA

Free DataManagers when a transaction becomes non-current.

added ITransactionManager.registeredSynchs and clearSynchs