One of the most appealing things about 1996’s “Trainspotting” was its smack-you-in-the-face vigor. In nearly every scene, and certainly in the film’s explosive introduction, director Danny Boyle and his attractive cast offered a sense that a strong (occasionally overworked) heart was pumping blood to all the film’s vital organs. The same kinetic camera work, hip soundtrack and alternately energized and melancholy editing supplies a ruddy character to the sequel, “T2 Trainspotting,” which revisits our heroin addicts in hardscrabble Edinburgh, and is again adapted from author Irvine Welsh’s work (in this case, the 2002 novel “Porno”). “T2” cannot help but live in the shadow of that same vigor, now recast as a sort of middle-aged exhaustion.