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