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
But pep8, [on pypi](https://pypi.python.org/pypi/pep8) seems to only have one file available for python 2. 
Sometimes, a package has a .tgz and .zip but they'd be both for python 2 (or both for python 3). I can't see this being the case for pep8.