David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, Ont. N2L 3G1, Canada. scli@uwaterloo.ca|David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, Ont. N2L 3G1, Canada. scli@uwaterloo.ca|David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, Ont. N2L 3G1, Canada. scli@uwaterloo.ca|David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, Ont. N2L 3G1, Canada. scli@uwaterloo.ca|David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, Ont. N2L 3G1, Canada. scli@uwaterloo.ca