Ensure that any created parent directories are made with `user`/`group`
perms, not as the `archive_user` user. This also allows setting the
group for these dirs instead of defaulting to `root`.

The `archive_user` argument to archive.extracted has been deprecated
since version 2014.7.2, and supplanted by the `user` parameter in
2015.8.0, with a logged warning until Boron. Now that 2016.3.0 is out,
complete the deprecation by:
- no longer silently using `archive_user` in `archive.extracted`,
  preferring instead `user` and `group`,
- no longer accepted `archive_user` as an argument.

Also update man page.