[1] M. Smoluchowski Institute of Physics, Jagellonian University, Cracow, Poland
[2] Fakultät für Physik, Universität Bielefeld, P.O. Box 100131, D-33501 Bielefeld, Germany
[3] Department of Mathematics, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
[4] Fortis Bank Polska S.A., Postepu 15, 02-676 Warsaw, Poland
[5] HAS Res. Grp. for Theor. Physics, Eötvös University, H-1518 Budapest, Hungary
[6] Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794