Message 244597 - Python tracker

(from msg244574 in issue16991)

crash-1.py is due to an unchecked return value from _odictnode_VALUE().

We should probably use PyDict_GetItemWithError(), also in other
places.

I normally try to steer clear of stylistic remarks, but the
_odictnode* macros are hiding too many things.  As of now,
they were hiding that an assert() is always true and that a
return value was unchecked.

Also, they're very inconvenient in a debugger.