'Quadruple witching' may spell some relief to stressed stocks

LONDON (Reuters) - In calm markets "quadruple witching" usually passes unnoticed, but some market players are hoping this Friday's concurrent quarterly expiration of U.S. options and futures contracts could shake some sense back into stocks.The expiration of stock options, stock index futures and index option contracts on the same day on the third Friday of the last month each quarter usually heralds hectic trading and volatility as investors unwind old positions and take new ones.But after one..