Gregory's Girl, Shallow Grave, Trainspotting... and now Hallam Foe. Starring Jamie Bell and filmed on location in Edinburgh, the new film from director David Mackenzie opened this year's Edinburgh International Film Festival to critical acclaim. But will it join the list of Scottish classics? And what is the recipe for cinematic success? With contributions from stars and film-makers including Martin Compston, Tilda Swinton, Ken Loach and Gillies