Discount Variety Retail Chain Dollar Tree reported that higher-income shoppers are contributing to one of its most successful recent quarters, fueling a resurgence for the retailer.  The retailer saw 3 million more households shop its stores during the third quarter compared to the prior year, and about 60% of those shoppers came from households earning over $100,000, equal to the combined share of middle-income households (earning $60,000 to $100,000 at 30%) and lower-income