Pred hashing not consistent with Pred equality

[goodmami]

The Pred component class compares with strings that may or may not end in _rel:

>>> p = Pred.stringpred('udef_q_rel')
>>> p == 'udef_q'
True
>>> p == 'udef_q_rel'
True
>>> p == '_udef_q'
False
>>> p == 'udef'
False

But this does not work with hashing (e.g. in a dict or set):

>>> Pred.stringpred('udef_q') in set(['udef_q', 'proper_q'])
True
>>> Pred.stringpred('udef_q_rel') in set(['udef_q', 'proper_q'])
False
>>> Pred.stringpred('udef_q') in set(['udef_q_rel', 'proper_q'])
False
>>> Pred.stringpred('udef_q') in set([Pred.stringpred('udef_q_rel'), Pred.stringpred('proper_q')])
False
>>> 'udef_q' in set([Pred.stringpred('udef_q_rel'), Pred.stringpred('proper_q')])
False
>>> 'udef_q_rel' in set([Pred.stringpred('udef_q_rel'), Pred.stringpred('proper_q')])
True
>>> any(Pred.stringpred('udef_q_rel') == q for q in set(['udef_q', 'proper_q']))
True

Hashing consistently on the short form would help when a Pred object is checked against Pred objects in a hash, but not when strings are used. I can't think of a good way around the latter issue, so maybe some documentation needs to be written about that.