[Checkins] [zopefoundation/zope.interface] edc67d: Test PURE_PYTHON at runtime.

[Jason Madden]

  Branch: refs/heads/no-pure-python-build
  Home:   https://github.com/zopefoundation/zope.interface
  Commit: edc67dfeb49060ce75563e32e45f5023e65c075b
      https://github.com/zopefoundation/zope.interface/commit/edc67dfeb49060ce75563e32e45f5023e65c075b
  Author: Jason Madden <jamadden at gmail.com>
  Date:   2020-01-21 (Tue, 21 Jan 2020)

  Changed paths:
    M .travis.yml
    M CHANGES.rst
    M setup.py
    M src/zope/interface/_compat.py
    M src/zope/interface/_zope_interface_coptimizations.c
    M src/zope/interface/adapter.py
    M src/zope/interface/declarations.py
    M src/zope/interface/interface.py
    M src/zope/interface/tests/__init__.py
    M src/zope/interface/tests/test_adapter.py
    M src/zope/interface/tests/test_declarations.py
    M src/zope/interface/tests/test_interface.py
    M tox.ini

  Log Message:
  -----------
  Test PURE_PYTHON at runtime.

Turns out that the C extensions build and work fine with PyPy, but don't use them by default. Let them
be forced, though.

Tests needed some refactoring to account for the various permutations.