Provide a pip-6.0 agnostic setup.py example

While this [commit](https://github.com/evansde77/cirrus/commit/8b4fb6d6b608f1124eebe899d0821abcdda94740) fixed the example for pip 6.0, it did so at the expense of previous pip version compatibility. Here I change our example to do a manual split and make the file pre/post pip 6.0 agnostic.

Here is the pip change which broke things: https://github.com/pypa/pip/commit/7037443975ee5706ef829f14a52ac2fba7dbfff2

Pip maintainers themselves recommend against using parse_requirements.
  - http://stackoverflow.com/questions/14399534/how-can-i-reference-requirements-txt-for-the-install-requires-kwarg-in-setuptool#comment34497476_16624700

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