Center for Biological Sequence Analysis, Technical University of Denmark, DK-2800 Lyngby, Denmark. massimo@cbs.dtu.dk|Center for Biological Sequence Analysis, Technical University of Denmark, DK-2800 Lyngby, Denmark. massimo@cbs.dtu.dk|Center for Biological Sequence Analysis, Technical University of Denmark, DK-2800 Lyngby, Denmark. massimo@cbs.dtu.dk