Department of Computing Science, University of Alberta, Edmonton, AB T6G2E8, Canada. bioinfo@cs.ualberta.ca|Department of Computing Science, University of Alberta, Edmonton, AB T6G2E8, Canada. bioinfo@cs.ualberta.ca|Department of Computing Science, University of Alberta, Edmonton, AB T6G2E8, Canada. bioinfo@cs.ualberta.ca|Department of Computing Science, University of Alberta, Edmonton, AB T6G2E8, Canada. bioinfo@cs.ualberta.ca