Initialize the ob_type field of PyAST_Type dynamically (in

initparser()) instead of statically (in the initializer).  The static
initialization, using the address of an object in a different DLL, is
too much for the Microsoft VC++ compiler, and we want to be able to
build this module as a separate DLL (it's nice to have but we don't
want to increase the core DLL's size by 25K).  This same trick has
been applied to a number of modules, e.g. NumPy and _tkinter.