[1] DESY, D-22603 Hamburg, Germany
[2] CERN, Div Theory, CH-1211 Geneva 23, Switzerland
[3] Florida State Univ, Supercomp Computat Res Inst, Tallahassee, FL 32306 USA
[4] DESY, IFH Zeuthen, D-15738 Zeuthen, Germany
[5] Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany
[6] Univ Oxford, Oxford OX1 3NP, England