PathFinder.distinct is based on file name, not path

If I have the following files:
- `a/b/foo.txt`
- `a/c/foo.txt`

And I do:

``` scala
file("a").***.distinct
```

I end up with only one file, even though there are two distinct paths, because the implementation of `distinct` matches on file name, not file path.

See https://github.com/playframework/playframework/issues/4208 for an example of issues this can cause.
