David Fincher says in Keanu Reeves’ doc on filmmaking, “Side By Side,” that Robert Downey Jr. was so peeved about putting in long hours on “Zodiac,” he left jars filled with urine around the set, in protest. (Fincher’s use of digital cameras meant less time for breaks.) Reeves unveiled his movie at MoMA on Thursday. He said at the Tribeca Film screening he wasn’t above begging to land interviews with Fincher, Christopher Nolan, James Cameron, Martin Scorsese and George Lucas.