This question, while somewhat old, recently had a 250 point bounty placed upon it by David E. Speyer. However, as I remarked in the comments, it has already been answered by Harry West, but in the context of another question (the answer is here — specifically, the part of his answer that begins with “if we can find” and ends with “old joke”).
In my mind, this clearly means that Harry West should get the bounty. But I'm not sure whether or how this can be done. (I'm not really involved in this, being neither the asker, nor the bountier nor the answerer, but I think it's worth raising the issue here, especially since there's no real way to notify other people on MathOverflow.)