It's enough to drive a coin collector crazy. The Senate has passed a bill six times to update the current designs of the backs of U.S. coins. The changes would likely raise millions from coin collectors. But the legislation keeps getting hung up in the House. Last year, sources say, the bill stalled because Diane Wolf, a former member of the Commission of Fine Arts who has pushed hard for the changes, rubbed key congressmen the wrong way. The delays have created a new problem: a leading design idea was to commemorate the bicentennial of the U.S. Constitution. That was more than two years ago.