Alex Gibney says Laurene Powell agreed to help – then tried to dissuade potential interviewees from taking partFour years ago, the death of Apple co-founder Steve Jobs triggered a global expression of mourning of a depth and duration that Oscar-winning documentary-maker Alex Gibney found hard to explain.Were the people who gathered at candlelit vigils at Apple stores around the world grieving for Jobs, or the perceived loss of a future that seemed to promise an endless procession of gadgets and devices each more extraordinary and innovative than the last?