[Checkins] [zopefoundation/AccessControl] 855089: Add support for Python 3.9.

[Michael Howitz]

  Branch: refs/heads/py39
  Home:   https://github.com/zopefoundation/AccessControl
  Commit: 8550893125cabe12f88adb6cc1a4f7400d3ea304
      https://github.com/zopefoundation/AccessControl/commit/8550893125cabe12f88adb6cc1a4f7400d3ea304
  Author: Michael Howitz <mh at gocept.com>
  Date:   2020-09-28 (Mon, 28 Sep 2020)

  Changed paths:
    M .travis.yml
    M CHANGES.rst
    M appveyor.yml
    M setup.py
    M tox.ini

  Log Message:
  -----------
  Add support for Python 3.9.

This PR requires a new release of RestrictedPython before being able to
be successful.