NTFS: - Change ntfs_cluster_alloc() to take an extra boolean parameter

NTFS: - Change ntfs_cluster_alloc() to take an extra boolean parameter
        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: Anton Altaparmakov <aia21@cantab.net>