We have now ditched AnchoredFile and just use File with Path Abs
in the path field.
This is useful since we now:
* don't allow "." or ".." as filenames anymore
* normalise paths in our path parsers and reject paths with ".."
This also allows us to know that filepaths are always valid. In addition
the 'basename' function from hpath may throw an exception if run
on the root dir "/". This exception is basically uncatched currently,
which is fine, because it's not a selectable directory.
