Merge branch 'python-pep-3147' into maint

* python-pep-3147:
  tests: fix a spurious failure when $PYTHON is in the environment
  python tests: support PEP-3147 installation layout
  python: uninstall cater to PEP-3147
  tests: improve a comment
  tests: honour $PYTHON override
  tests: typofix in message
  news: document fix for bug#8847 (PEP-3147, __pycache__)
  python: improve support for modern python (CPython 3.2 and PyPy)

diff --cc NEWS
Simple merge