https://www.python.org/downloads/release/python-352/

Runtimes:
* Added pypy-5.3.0
* Moved python-2.7.11rc1 to python-2.7.12rc1

clean up pip-grep in the `not silent` case

remove Pylibmc reference in cryptography comment

Use Travis

Added another package that relies on cffi

The extraneous `format` call is harmless in itself, but it's possible for `requirement.req` to be `None` here, which results in `AttributeError: 'NoneType' object has no attribute 'project_name'`.

Add PyNaCl to the list of packages that trigger libffi bootstrapping

To reduce confusion for users who have not explicitly listed cffi as a
dependency.

Fixes #142.

Add PyPy 5.0.1

Keep pre-existing environment variables.

`PKG_CONFIG_PATH` variable.

Update pip and setuptools

Update buildpack image to align with marketing

https://pythonhosted.org/setuptools/history.html
https://bitbucket.org/pypa/setuptools/branches/compare/20.2.2%0D19.6

The release on PyPI isn't signed, though the MD5 of this archive matches
that on the PyPI package page:

$ md5sum setuptools-20.2.2.tar.gz
bf37191cb4c1472fb61e6f933d2006b1 *setuptools-20.2.2.tar.gz