This is my contribution to the proceedings of the conference "Relativity and Gravitation: 100 Years after Einstein in Prague" held June 25—29, 2012, in Prague, Czech Republic. It is based on my refereed-journal paper of the same title.
A review of the excellent proceedings by Lars Andersson mentions my contribution.
The links below point to one file containing the complete text, all figures and tables etc.
As are most of my publications this is available in more than one form: