UPDATE with PricewaterhouseCoopers statement: The Best Picture gaffe that marred tonight’s Oscar broadcast was caused by a doppelganger Best Actress envelope mistaken for the night’s final prize, which caused the unprecedented screw-up that temporarily bestowed the top trophy to La La Land instead of rightful winner Moonlight. Accounting firm PricewaterhouseCoopers confirmed just now that the fault was theirs: We sincerely apologize to Moonlight, La La Land, Warren…