US STOCKS-Wall St slips on Spain, earnings worries

* Markets volatile about uncertain Spain bailout * Shares of Chipotle fall after comments by fund chief Einhorn * PetSmart rises before joining S&P 500 index * Indexes down: Dow 0.5 pct, S&P 0.2 pct, Nasdaq 0.1 pct By Angela Moon NEW YORK, Oct 2 (Reuters) - U.S. stocks edged lower in a volatile session on Tuesday over uncertainty about a financial bailout for Spain and investor worries that third-quarter U.S. earnings will disappoint. The Dow was pressured by stocks cl