SAN MARCOS — The scale is difficult to absorb.Three panels from Buck Winn’s giant recovered 1950 mural "The History of Ranching" were recently installed at Texas State University in San Marcos. At a combined 82 feet long — once part of a 280-foot cylindrical mural — the pictures arc gloriously over the welcome desk at the Alkek Library, a modernist tower without much exterior charm but with lots of space and light inside.In a style that reminds one of post office murals