PEP 3121 at python.org mentions PyType_Copy().  However, it doesn't seem
to be present in SVN version and there is no apparent replacement. 
Please clarify how types should be created for different module
instances --- if just sharing is fine, or should some copying (which
function?) be used.

The intention is that different interpreters have distinct, separate
instances of the type objects. This is desirable in case of class
variables, and standard for Python-defined types. Clearly, 3.0 won't
provide that separation for many of the builtin types (and never may);
for out-of-core types, it is really the choice of the module designer.

I forgot to implement PyType_Copy; it is meant to create a new type
object which is a field-by-field copy. It's now too late to add it to
3.0; extension authors requiring it now should include it's source code
(which is currently not even written - contributions are welcome).

Reconsidering it: what should it do to the base types? 
 a) just incref tp_base and clone tp_bases, 
 b) offer an optional parameter to specify an alternative base object, 
 c) offer an optional parameter to specify an alternative bases tuple.