Pictured above is my T-shirt from the 1997 HFStival. That was back when 99.1 still ruled the D.C. alt-rock airwaves, and the festival was the be-all-end-all musical event of the year. Going was a right of passage for which I had to beg my parents’ permission for years. On September 18 at Merriweather Post Pavilion, local teenagers will get the chance to feel completely differently than I did about much the same lineup: MAIN…