Add __reduce__() method to BitwiseOperator and _NamedInt.

Add __reduce__() method to BitwiseOperator and _NamedInt.

This makes it possible to successfully pickle and deepcopy instances
of these types [1,2].  This gets the

  TRIG_SRC.now == copy.deepcopy(TRIG_SRC.now)

doctest working, which I needed to successfully dump h5config
ChoiceConfig objects that use _Enum choices [3].

For example, the newly fixed pypiezo.config.ChannelConfig [4] uses the
AREF enum values as possible choices for it's `analog-reference`
setting.  h5config makes deepcopies of mutable objects to avoid
confusion if the mutable is changed externally.  It then compares the
deepcopies with uncopied values.  Now that deepcopying works for
_NamedInts, the h5config behavior will work.

[1] http://docs.python.org/library/pickle.html#pickling-and-unpickling-extension-types
[2] http://docs.python.org/library/copy.html
[3] http://pypi.python.org/pypi/h5config/
[4] http://pypi.python.org/pypi/pypiezo/