David Abrahams tried to compile this as a separate DLL under MSVC, and

David Abrahams tried to compile this as a separate DLL under MSVC, and
got a barrage of compile errors that didn't make sense to the C++ brain:
MSVC does not allow C (but does allow C++) initializers to contain
data addresses supplied by other DLLs.  So changed the initializers here
to use dummy nulls, and changed module init to plug in the foreign
addresses at runtime (manually simulating what C++ does by magic).  Tested
on Windows, and Guido tested on Linux (thanks!).  BTW, the *point* is that
people are going to use this module as a template for writing their own
subtypes, and it's unusual for extension authors to build their extensions
into Python directly (separate DLLs are the norm on Windows); so it's
better if we give them a template that works <wink>.