Add Python 2.7.12, Python 3.5.2, Pypy 5.3.1, Pip 8.1.2, Setuptools 23.1.0 and remove release candidate

* $ curl
https://pypi.python.org/packages/e7/a8/7556133689add8d1a54c0b14aeff0acb0
3c64707ce100ecd53934da1aa13/pip-8.1.2.tar.gz -o pip-8.1.2.tar.gz
* $ curl
https://pypi.python.org/packages/9f/7c/0a33c528164f1b7ff8cf0684cf88c2e73
3c8ae0119ceca4a3955c7fc059d/setuptools-23.1.0.tar.gz -o
setuptools-23.1.0.tar.gz
* $ ls
* $ rm pip-8.1.1.tar.gz
* $ rm setuptools-20.4.tar.gz

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.