- Allow the syntax "specials=True" to indicate that a type variable can
assume all special types. Use this for the unconstrained type variable
created in ast.py.
- Fix TypeSet.copy() to avoid deepcopy() which doesn't do the right
thing for the self.specials set.
- Fix TypeSet.typeset_key() to just use the name of special types
instead of the full SpecialType objects.
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