Fileservice: Should use FULL paths

[Nick Chadwick]

At the moment FileService works on a strange kind of path based at
/home/$USER in the users jail. While there are some good reasons for hiding
the full path from users (at least until the understand the Unix home
directory concept) forcing the client to operate on these paths just fills
the interfaces with a horrible mess of special cases to add/remove the
/home/%USER prefix.

FileService as a relatively low interface should always work on full jail
paths and the client should make the decision when and if to hide any of
the path.

[William Grant (wgrant)]

This is going to be affected by the future possible RESTification, so dropping the
priority. Do not work on this for now.