Issue #17576: Deprecation warning emitted now when __int__() or __index__()
return not int instance.  Introduced _PyLong_FromNbInt() and refactored
PyLong_As*() functions.
#19063: partially fix set_payload handling of non-ASCII string input.

This is a backward compatible partial fix, the complete fix requires raising
an error instead of accepting the invalid input, so the real fix is only
suitable for 3.4.
Issue #19828: Fixed test_site when the whole suite is run with -S.

Also, cleaned up an unused import.
Filter namespaceobject's files properly in the pythoncore VS project.