After taking his Dive Bar Tour to Chicago (July 15) and Bakersfield (Aug. 15), Garth Brooks announced the third stop on his seven-date tour: Gruene Hall in New Braunfels, Texas, on Sept. 23. Built in the 1870s and known as the oldest continually run dancehall in the state, the 6,000-square-foot Gruene Hall is featured on…