[Pyrex] externs for python base types

[Greg Ewing]

David McNab wrote:
> it doesn't have the list internals structs sufficient to
> help one create an extension type subclassed from list

If you declare it inside an "extern from" block, this shouldn't
matter so much, since the C compiler will get the struct
members from the .h file (assuming such a .h file exists,
which it should do for most of the builtin types).

--
Greg