NameMapper issues with Google App Engine db.Model objects

In AppEngine, db.Model objects unfortunately implement a "has_key()"
method that checks if a model instance has had a key assigned to it
yet.

This causes NameMapper.py to determine that it should use dictionary
style access instead of getattr().

I think there are two possible solutions:
 1. use hasattr(obj, "keys") instead of hasattr(obj, "has_key")
 2. try to use hasattr()/getattr() ... before trying dictionary access

I tested #1 and it seems to work...but I'm too new to Cheetah to know
if there are unintended consequences

For #2 the biggest issue I see is in _valueForName() ... you
definitely don't want to hit the exception on every access to a
dictionary, so you'd need another call to hasattr()  ... which
presumably was just done before getting to _valueForName() in the
first place.

Probably not a big deal either way. I'm not sure if there was a
pre-existing design decision to try dictionary access before attribute
access.

- Chad

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