CANADA STOCKS-TSX drops on U.S. economic data; down for fifth day

* TSX down 139.75 points, or 0.92 percent, at 14,980.79 * Nine of the 10 main index sectors decline * Valeant shares jump after ValueAct executive to join board By John Tilak TORONTO, Sept 25 (Reuters) - Canada's main stock index dropped for a fifth straight session on Thursday, nearing a three-month low, as sluggish U.S. economic data weighed on sentiment. Market volatility shot up and commodity prices remained choppy. A decline in the price of bullion sent gold-mining shar