Paths are left as paths, instead of trying to convert them to strings
or byte strings. Submodule path elements should be unquoted -- in the
same form as a `submod' form. All extra parts are submodule path elements,
never module paths or ".".
`setup/private/path-utils'.
The API is a little different: instead of getting the alist and the
path, there's a curried function that gets the alist and produces a
function to do the substitutions.
