specifying whether the cluster are being allocated to extend an
        attribute or to fill a hole.
      - Change ntfs_attr_make_non_resident() to call ntfs_cluster_alloc()
        with @is_extension set to TRUE and remove the runlist terminator
        fixup code as this is now done by ntfs_cluster_alloc().
Signed-off-by: NAnton Altaparmakov <aia21@cantab.net>