fix bug 1047020 - Add Wheel Hashes to Requirements

Pins pep8 at 1.5.7 (The current tarball hash), and adds hashes for pep8 and pyflakes wheels.

Fixes bug 1047020
I'm confused. If the requirements file specifies `==` it won't install anything other than exactly `1.5.7`. No? So why bother having any other sha in there?