Ambition is not a problem for Danny Boyle. Humility might be. The Oscar-winning director of “Slumdog Millionaire” and “28 Days Later” is known for his lyrical and invigorating films, starting with his darkly comic 1994 debut “Shallow Grave” and continuing with 1996’s “Trainspotting,” the U.K. crossover hit that endeared a young Ewan McGregor to audiences around the world. But when it came to following up “Trainspotting” with a sequel — adapted from the source material by Scottish novelist Irvine Welsh — Boyle and “Trainspotting” screenwriter John Hodge learned a hard lesson. “We tried to adapt it ten years ago after Irvine published his ‘Porno’ book (the literary sequel to ‘Trainspotting’) and we didn’t do it, because it wasn’t good enough,” said Boyle, 60.