Beijing turbocharged its auto market last year by slashing sales taxes on small cars and rolling out its own cash-for-clunkers plan to persuade drivers to junk the dirtiest models. It worked. Chinese drivers bought a record 13 million cars and light trucks last year, propelling that nation ahead of the United States as the world's largest auto market. Incentives are still in place this year, with the clunker buyback deal getting even sweeter. That