Testfixtures

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- Fix bug where :meth:`testfixtures.datetime.MockDateTime.now` didn't accept the `tz`
parameter that :meth:`datetime.datetime.now` did.

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- Give more useful output when comparing dicts and their subclasses.

- Turn :class:`should_raise` into a decorator form of
:class:`ShouldRaise` rather than the rather out-moded wrapper
function that it was.

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- Remove dependency on ``zope.dottedname``.

- Implement the ability to mock out :class:`dict` and :class:`list`
items using :class:`~testfixtures.Replacer` and
:func:`~testfixtures.replace`.

- Implement the ability to remove attributes and :class:`dict`
items using :class:`~testfixtures.Replacer` and
:func:`~testfixtures.replace`.

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- Fix for issue 328: :meth:`~testfixtures.datetime.MockDateTime.utcnow` of :any:`test_datetime <mock_datetime>`
now returns items from the internal queue in the same way as
:meth:`~testfixtures.datetime.MockDateTime.now`.

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- Fix bug when :class:`ShouldRaise` context managers incorrectly
reported what exception was incorrectly raised when the incorrectly
raised exception was a :class:`KeyError`.

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- Added ``TestComponents`` for getting a sterile
registry when testing code that uses ``zope.component``.