WASHINGTON (AP) - Supermarket checkout clerks are going the way of the bank teller - available if you want one, avoidable if you don't. Self-checkout machines, which let customers scan, bag and pay for their own groceries, offer shoppers a chance to avoid the lines at the checkout stands. "This is like an ATM for them. It's quicker and easier," said Jennifer Panetta, a spokeswoman for the six-state Harris Teeter chain, based in Matthews, N.C. "They are in pretty much all our stores." About one-quarter of grocery chains are trying them now, with some 34,000 machines in use in stores...