Add rudimentary support for saving AFS acls.

Add rudimentary support for saving AFS acls.

    Add support for saving and restoring AFS acls using the
    pioctl interface of (Open)AFS. This is mostly a proof of
    concept its no where ready for production and may put
    a enormous load on your AFS cell so please use it only
    for testing. It also only solves part of the AFS backup
    problem as we only save and restore acls on directories
    on an AFS filesystem but not the actual cell configuration
    etc. For that we advice you to use the native tooling
    using some script or the bpipe plugin.