Tipped for their first UK number one album with 'Sleep Well Beast', The National are about to turn from rock's biggest cult band into would-be Glastonbury-headliners. Andrew Trendell talks to the band about anxiety, evolution, Neo-Nazis, and "getting a bear-hug from Dave Grohl" The National's Matt Berninger For 18 years, The National have been playing the long game. They were outsiders in the days of the rock …