Bioinformatics Unit, Department of Computer Science, University College London, Gower Street, London, WC1E 6BT, UK. d.corney@cs.ucl.ac.uk|Bioinformatics Unit, Department of Computer Science, University College London, Gower Street, London, WC1E 6BT, UK. d.corney@cs.ucl.ac.uk|Bioinformatics Unit, Department of Computer Science, University College London, Gower Street, London, WC1E 6BT, UK. d.corney@cs.ucl.ac.uk|Bioinformatics Unit, Department of Computer Science, University College London, Gower Street, London, WC1E 6BT, UK. d.corney@cs.ucl.ac.uk