objects which have type checks in __eq__ or __cmp__ break serialization

[ccx@…]

Python classes that raise exceptions on comparison (== operator) may break the serialization as yaml/representer.py:142 contains:

if data in [None, ()]:

It should instead read:

if data is None or data is ():

to avoid invoking the class-defined comparison operations and check for object identity instead.

This currently breaks serialization of numpy.Array classes.