Center for Biological Sequence Analysis (CBS), Technical University of Denmark, Building 208, 2800 Lyngby, Denmark. laurent@cbs.dtu.dk|Center for Biological Sequence Analysis (CBS), Technical University of Denmark, Building 208, 2800 Lyngby, Denmark. laurent@cbs.dtu.dk|Center for Biological Sequence Analysis (CBS), Technical University of Denmark, Building 208, 2800 Lyngby, Denmark. laurent@cbs.dtu.dk|Center for Biological Sequence Analysis (CBS), Technical University of Denmark, Building 208, 2800 Lyngby, Denmark. laurent@cbs.dtu.dk