It's a once-in-a-lifetime theatrical event: Ian McKellen and Patrick Stewart are on stage together in Waiting For Godot. They discuss how this casting to die for came about.The prospect of seeing Sir Ian McKellen, the pre-eminent male classical actor of his generation, treading the boards again is in itself enough to warrant a box-office stampede. The prospect of seeing him star in Waiting for Godot opposite Patrick Stewart, who is fast catching up with him in the theatrical titan stakes after a long sojourn in LA playing Capt Jean-Luc Picard in Star Trek, is a once-in-a-lifetime excitement. Literally so, since...