1. Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg, Germany
2. Astronomy Department, Yale University, PO Box 208101, New Haven, CT 06520-8101, USA
3. Department of Astronomy and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720-3411, USA
4. Department of Physics and Astronomy and CIERA, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
5. Department of Physics, Center for Astrophysics and Space Science, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
6. TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125, USA
7. Institute for Computational Science, University of Zurich, CH-8057 Zurich, Switzerland