setup.py should always pass pyflakes

[jayvdb]

Spawned from #81

Relevant pyflakes rules are no unused variables/imports.

Fixing unused variables is simply about template logic considering the moban variables before emitting the header of the .py file.

The template logic may get a tiny bit complex for imports, as there are several import styles, but this issue isnt about the style, as pyflakes doesnt care about that. However, the solution shouldnt be worse import style than the current code, so a little care is needed.