The most dangerous way to sell short is to pick a hot little stock that’s “way overvalued” and bet that it will come down. Such a case in recent weeks has been American Superconductor (AMSC), a company that recently found new life by entering the market for wind energy. For the past five months, AMSC’s chart, in climbing from 16 to 45, has rewarded investors who were long on the stock, and it has punished short-sellers ... despite the broad market being unsupportive.