Pass relative path to .hotpot.lua build/clean functions

[rktjmp]

The root path "type" given to api.make is inherited by paths given to any "build functions".

This makes some sense when using api.make.build because the root path is explicitly given by the user, and so a relative path is relative to the cwd, and returned paths should also be relative to the cwd, or if given an absolute path, the returned paths should also be absolute.

A .hotpot.lua file is intrinsically "relative" to the dir its inside, but when discovering the .hotpot.lua files container dir, we resolve it to an absolute path, which means the paths passed along end up being absolute instead of relative.