NEW YORK (TheStreet) -- While it's hard to predict the markets, when it comes to the month of May, one thing is for certain: You'll hear someone say, at least once, "sell in May and go away." The cliché, which suggests that smart investors should sell off their portfolios in May and only re-enter the market in the fall, has long been part of Wall Street culture, but where does it come from? The saying dates back to old England, when the stock brokers would go on summer vacation in May and not return until September. The original saying was,...