Nostalgia, as they say, ain’t what it used to be. Two decades on from the incendiary Trainspotting (1996), T2: Trainspotting (18s) finds ex-junkies Mark (Ewan McGregor), Sickboy (Jonny Lee Miller), Spud (Ewen Bremner) and Begbie (Robert Carlyle) converging again on Edinburgh’s mean streets.