1. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309, USA
2. Linac Coherent Light Source, SLAC National Accelerator Laboratory, P.O. Box 20450, Stanford, California 94309, USA
3. Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden