use filepath instead of path

[thaJeztah]

Originally, this package was documented to be for paths separated by forward slashes, but I was recently pointed to the updated package description, which amended the documentation (see https://go-review.googlesource.com/32423) and added:

To manipulate operating system paths, use the path/filepath package.

A later patch (https://go-review.googlesource.com/45653) tweaked the description again, adding to the path/filepath package:

To process paths such as URLs that always use forward slashes regardless of
the operating system, see the path package.

And to the path package

This package does not deal with Windows paths with drive letters or backslashes;
to manipulate operating system paths, use the path/filepath package.

I expect it to be "fine" in general to use the path package for Unix/Linux, but
from both patches, the intent of the Go maintainers is to use path/filepath
for anything file(system) related, so let's adapt to that.

[rhatdan]

LGTM
@kolyshkin @giuseppe @lsm5 PTAL

[kolyshkin]

I am slightly more inclined towards using path rather than filepath, as path is somewhat simpler, and will definitely work fine on Linux (and this code is Linux-specific and will stay that way).

OTOH I don't see a reason to not use filepath, so LGTM.

[thaJeztah]

Yup; I originally thought "path" was the way to go as well. Fun fact (but I need to give it another go), was that I did some benchmarking at some time, and filepath was more performant than path (perhaps they added some optimisation that they didn't add to path ?

Also if their intent is for filepath to be used for file paths, then there is "some" risk that path may be missing some (obscure?) handling for file-specifics, or at least their focus may not be on that, so using filepath would be the safer option I guess?