SYNOPSIS:
    MARKCG_NEARBY fromgrey togrey mindist fromset toset [greyset]

DESCRIPTION:
    Remark all voxels of fromset, that have greyvalue entries
    within mindist that are within the window defined by
    fromgrey/togrey. Only voxels that are in [greyset] are taken
    into account when looking for grey values.
    greyset defaults to 0-31 (standard reserved range for grey values).
