Hedge funds have built up their biggest bet against the yen in 17 years, raising the prospect that when Japan’s embattled currency does rebound from its 34-year low against the dollar, the short-covering rally could be a powerful one. The latest Commodity Futures Trading Commission data show that speculators’ net short yen position is the largest since June 2007, and one of the biggest since yen futures contracts were launched in 1986. The yen is down nearly 9% against the dollar since Jan. 1, making it the worst-performing G10 currency this year. The Swiss franc is down almost as much, but the Swiss National Bank ... (full story)