[PATCH evolve-ext v2] py3: broad pass for python3 compatibility

[Ludovic Chabant]

> 
> Should opts[x], opts.get(x), etc really use bytes? They usually get passed as **opts, which means their keys are str, I think.
> 

Sounds OK to me -- there's probably a whole bunch of places that might need to be excluded. It might be worth exploring doing the opposite approach, i.e. manually adding byte strings until things work.