For more than a year, hedge funds have held a bearish position in U.S. natural gas, betting that a ballooning supply glut would hammer prices. Just before gas futures tumbled to a 17-year low this week, money managers boosted their net-short position in contracts for the fuel by 31 percent. Their bearish bets jumped in the seven days ended Feb. 23 while their long wagers on prices rising were little changed,...