CANADA STOCKS-TSX tumbles to three-month low as sentiment sours

* TSX down 226.97 points, or 1.5 percent, at 14,893.57 * Eight of the 10 main index sectors decline * Valeant shares jump as ValueAct executive to join board By John Tilak TORONTO, Sept 25 (Reuters) - Canada's main stock index dropped 1.5 percent on Thursday, its worst fall in 7-1/2 months, as negative sentiment for equities and choppy commodity prices helped drag down shares in most major sectors. Investors brushed aside data showing that new orders for capital goods by U.