Review: “An Inquiry into the Poverty of Nations.” : By Gunnar Myrdal. Assisted by William J. Barber, Altti Majava, Alva Myrdal, Paul P. Streeten, David Wightman and George W. Wilson. 3 Volumes, Charts and Tables, 2,284 Pp. The Twentieth Century Fund, New York, Cloth, Boxed, $25. Pantheon Books, New York