Fix various warnings/errors detected by PyLint

[JeremyRand]

One of the fixes was in platform-dependent code, someone please test to make sure it still boots without exceptions on Windows.

[phelixbtc]

I would not remove this, it helps readability. As long as we don't remove this global we should at least be explicit about it.

[JeremyRand]

We never write to app; PyLint therefore complains that we shouldn't declare it as a global, since the only reason to declare as a global is so that you can write to it. I don't think it makes things more readable either (and it makes the code less readable to PyLint).

[phelixbtc]

Why do you suggest to convert all the option dicts to lists?

[JeremyRand]

@phelixbtc Khal's code was converting dicts to lists at run time (but also accepted lists verbatim); that makes it impossible for PyLint to do static analysis of that code to check for errors.

[phelixbtc]

FTFY: #83

[JeremyRand]

Now that #83 is merged, I'll rebase this soon to not include that particular fix.