BY JONATHAN VALANIA FOR THE INQUIRER Funny how Gen X used to mercilessly mock its predecessors for endlessly revisiting the Woodstockian ecstasies of its youth, as though nostalgia were a generational affliction instead of a universal symptom of aging. Now that the gray-bearding of Gen X has commenced, its members have proved no less immune to the impulse to revisit the pleasures of their gloriously misspent youth. Exhibit A is Guided by Voices’ sold-out “Hallway Of Shatterproof Glass Tour,” which reunites the so-called classic lineup of the Dayton, Ohio, indie darlings for one more beery, fist-pumping, scissors-kicking sing-along of their underground anthems from the mid-1990s. The tour’s stop at the Trocadero on Saturday night had been sold out almost since the moment it was announced months before. MORE