Goldman Sachs forecasts that its commodity index will earn 6 percent over the coming 12-month period. That may be a welcome prediction, or one brushed off as unserious. After all, those investing in commodities over the past decade have certainly not found them rewarding. But Jason Zweig of the Wall Street Journal noted in a recent article that money can be made in commodities, but only by the most patient of investors.  Zweig cites analysis by SummerHaven Investment Management LLC, which reviewed futures contracts over the past nearly 150 years and found they outperformed cash and inflation by 5.2 percent. That is just behind the average 5.5 percent earned by stocks over the past 118 years. The narrow difference is surprising given t...