Close #14857: fix regression in references to PEP 3135 implicit __class__ closure variable. Reopens issue #12370, but also updates unittest.mock to workaround that issue

Fixes up minor descrepancies with cPython initial import.

(PyTypeObject, PyMethodDescr_Type, _PyMethodWrapper_Type, and
PyWrapperDescr_Type) have been modified to provide introspection
information for builtins.  Also: many additional Lib, test suite, and
Argument Clinic fixes.

Author: Larry Hastings <larry@hastings.org>

- .travis.yml
- update README.txt about testing
- setup.py hard-depends on setuptools to get extras support.