Department of Applied Statistics, JK University Linz, A-4040 Linz, Austria, Institute of Mathematics, Technische Universität Ilmenau, D-98693 Ilmenau, Germany, Institute for Mathematical Stochastics and Felix Bernstein Institute for Mathematical Statistics in Biosciences, Georgia Augusta University of Goettingen and Max Planck Institute for Biophysical Chemistry, D-37077 Goettingen, Germany.