Contact info T. Menzies is with the Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV 26506-610. E-mail: tim@menzies.us. 304 376 2859 J. Andrews and F. Li are with the Department of Computer Science, University of Western Ontario, London, Ont., Canada, N6A 2B7. E-mail: andrews@csd.uwo.ca.