Commentslatex 21 pages, 11 figures; Invited talk at the 14th international workshop on General relativity and Gravitation, Yukawa Institute for Theoretical Physics, Nov 29-Dec 3, 2004, Kyoto, Japan. An important comment added in section 6; additional references
Journal refProceedings of the 14th Workshop on General relativity and Gravitation (JGRG14), Kyoto University, Japan 29 November - 3 December, 2004. Edited by W. Hikida, M. Sasaki, T. Tanaka and T. Nakamura; p 95 - 115.
CommentsLaTeX, 14 pages, talk given at Bryce DeWitt memorial session of the International Conference on Theoretical Physics, 70 years Jubilee of the I.E.Tamm Theory Department of the Lebedev Physics Institute, Moscow, April 11-16, 2005