7-11 Adopting Wireless Technology By DAVID KOENIG     ROCKWALL, Texas (AP) -- Sherry Neal checked the refrigerated shelves of her 7-Eleven store, touched the screen of a small handheld computer and got an instant four-week sales history on turkey sandwiches.    With a couple taps on the wireless device, the store manager placed an order for the next day's sandwiches without ever leaving the aisle...