Computatational Biology Department, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, USA. troman@andrew.cmu.edu.|Computer Science Department, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, USA. amirn@cmu.edu.|Department of Computer Science, Tulane University, 6834 St. Charles St., New Orleans, USA. bfasy@tulane.edu.|Computatational Biology Department, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, USA. russells@andrew.cmu.edu.