After three years of dismal performance and lack of investor interest, Dent Tactical ETF (DENT), the brainchild of Harry Dent -- founder of economic forecasting and research firm HS Dent -- is shutting down Wednesday. AdvisorShares, best known for providing actively managed ETFs, is liquidating it -- a little more than a month before its third birthday. DENT's manager resigned in June, when Laif Meidell, who manages AdvisorShares Meidell Tactical