Update py-setuptools to 19.6.1. All self-tests pass.

19.6.1
------

* Restore compatibility for PyPy 3 compatibility lost in
  19.4.1 addressing Issue #487.
* ``setuptools.launch`` shim now loads scripts in a new
  namespace, avoiding getting relative imports from
  the setuptools package on Python 2.

19.6
----

* Added a new entry script ``setuptools.launch``,
  implementing the shim found in
  ``pip.util.setuptools_build``. Use this command to launch
  distutils-only packages under setuptools in the same way that
  pip does, causing the setuptools monkeypatching of distutils
  to be invoked prior to invoking a script. Useful for debugging
  or otherwise installing a distutils-only package under
  setuptools when pip isn't available or otherwise does not
  expose the desired functionality. For example::

    $ python -m setuptools.launch setup.py develop

* Issue #488: Fix dual manifestation of Extension class in
  extension packages installed as dependencies when Cython
  is present.

19.5
----

* Issue #486: Correct TypeError when getfilesystemencoding
  returns None.
* Issue #139: Clarified the license as MIT.
* Pull Request #169: Removed special handling of command
  spec in scripts for Jython.

19.4.1
------

* Issue #487: Use direct invocation of ``importlib.machinery``
  in ``pkg_resources`` to avoid missing detection on relevant
  platforms.

(wiz)