Reducing CPP

[Ericson2314]

We have a lot of CPP at the moment, and I think Eelco wanted it reduced. Perhaps we leverage things like the new C++ STL filesystem API to reduce it? If possible, we could land such changes first, too.

[Ericson2314]

Absolutely! I think that's the best shot to keep things maintainable, and I want things like linux<->windows remote building. I also help this make Nix easier to port to still more systems since the Unix stuff will need to be abstracted a bit.

[Ericson2314]

Oh if Boost doesn't give us that....bummer. OTOH now that there is a Path vs StorePath distinction, that might make some interop earlier, e.g. if eval-time is restricted to paths which are in the form StorePath / option valid unicode relative path?