Bringing China In From the Cold By NICHOLAS D. KRISTOF [T] he loopiest aspect of the Group of 8 conclave in Évian is the notion that global leaders are confronting the challenges of the 21st century in the absence of the nation that may well dominate the century. That's right: China. Even if China's gross domestic product is measured using its official, undervalued exchange rate, its economy is far bigger than those of G-8 members like Canada or Italy ? and almost three times the size of Russia's. If one values China's economy using another approach, purchasing power parity, then...