Bespectacled pitmaster Milam Lamar wears a bandolier of barbecue sauce bottles, and his apron is weighed down by several bottles of Shiner Bock. He carries a canister of kerosene and a box of matches as he approaches a massive pit dug into the earth. Lamar is preparing a barbecue feast to celebrate the impending nuptials of Gutrune and Siegfried. If you recognize those two names, then you probably know the wedding plans are about to get derailed, and that the ring Siegfried carries is the namesake of nineteenth-century German composer Richard Wagner’s four-opera Ring cycle. This version, playing at Stages in Houston through June 1, happens to be set in Texas.In Das Barbecü, Wagner’s fifteen-hour opera series is condensed into two hours (with a fifteen-minute…