Economist: IN JUNE last year Daniel Avelino, the public prosecutor of Brazil’s state of Pará, the home of most of the Amazon cattle-herd, probably saved more rainforest than many conservation groups ever will. He identified 20 big ranches operating on illegally cleared land and traced the slaughterhouses buying their cattle. He then established that some of the world’s best-known retailers, including Wal-Mart and Carrefour, were buying meat from them. He fined the ranchers and abattoirs 2 billion reais …