If Vladimir and Estragon, the hapless protagonists of Samuel Beckett's "Waiting for Godot," had attempted to make a comedy sketch show, they might have ended up with something like "A Pigeon Sat on a Branch Reflecting on Existence." This mordant, strikingly original work from Swedish director Roy Andersson is a veritable theater of the absurd, executed with technical mastery and a healthy dose of glumness.