Bioinformatics Laboratory, Computer Science Department, University of Waterloo, N2L 3G1, Canada. mli@wh.math.uwaterloo.ca|Bioinformatics Laboratory, Computer Science Department, University of Waterloo, N2L 3G1, Canada. mli@wh.math.uwaterloo.ca|Bioinformatics Laboratory, Computer Science Department, University of Waterloo, N2L 3G1, Canada. mli@wh.math.uwaterloo.ca|Bioinformatics Laboratory, Computer Science Department, University of Waterloo, N2L 3G1, Canada. mli@wh.math.uwaterloo.ca|Bioinformatics Laboratory, Computer Science Department, University of Waterloo, N2L 3G1, Canada. mli@wh.math.uwaterloo.ca|Bioinformatics Laboratory, Computer Science Department, University of Waterloo, N2L 3G1, Canada. mli@wh.math.uwaterloo.ca