Bioinformatics Research Group, SRI International, EK223, 333 Ravenswood Ave, Menlo Park, CA 94025, USA. pkarp@ai.sri.com|Bioinformatics Research Group, SRI International, EK223, 333 Ravenswood Ave, Menlo Park, CA 94025, USA. pkarp@ai.sri.com|Bioinformatics Research Group, SRI International, EK223, 333 Ravenswood Ave, Menlo Park, CA 94025, USA. pkarp@ai.sri.com