Panera Bread (PNRA) and Chipotle Mexican Grill (CMG) report earnings after the market close Tuesday. Not long ago, those results would whet investors' appetites. But today there are several other eateries with better ratings. Krispy Kreme Doughnuts (KKD) knows all about getting stale. The donut chain exploded as an IPO in April 2000 just as the dot-com bubble was bursting. The stock ran up until the end of 2001 as the chain rapidly expanded out of