Scripts pass pyflakes, Travis tests it

I'm not a fan of how strict pep8 is, but pyflakes is sweet. It told me to get rid of lots of unused variables and imports, and caught a couple of bugs-in-waiting.

This fixes up all scripts to raise no pyflakes errors, and has Travis run pyflakes over them after running `test/workout.py`.

Thanks to @hugovk for the inspiration here!