Department of Computer Science and Engineering, University of California at San Diego, La Jolla, CA 92093-0114, USA. aprice@cs.ucsd.edu|Department of Computer Science and Engineering, University of California at San Diego, La Jolla, CA 92093-0114, USA. aprice@cs.ucsd.edu|Department of Computer Science and Engineering, University of California at San Diego, La Jolla, CA 92093-0114, USA. aprice@cs.ucsd.edu