“For the last five years, Pixar has been on quite a roll, churning out one reliably solid animated film every summer. The last four have won Oscars for Best Animated Feature, and the last three (WALL-E, Up, and Toy Story 3) are, in my mind, stone cold classics.  This winning streak and reputation for quality are what make Pixar’s latest, “Cars 2,” not just disappointing, but puzzling.”