Billy Crystal is getting schooled by Pixar — and he couldn’t be happier about returning to the “Monsters Inc.” universe and working again with fellow beastie John Goodman . “We’re having a blast together,” Crystal said Friday after a marathon recording session for “ Monsters University ,” which is planned for summer of 2013. “It’s really a great script, it’s really funny.” “That’s why I’m a little hoarse. I spent five-and-a-half hours today for our fourth session on ‘Monsters Inc. 2.’ And I have to tell you something, it is hilarious. The Pixar people are geniuses. It’s 10 years since the first movie. Yeah, it’s crazy. And it’s a prequel. They’re in college. It’s how they met, it’s how Michael and Sully meet, and plan to become scarers at Monsters Inc. — so this movie ends where the other one starts.” Crystal was on stage Friday night at a 20th anniversary screening of “City Slickers,” where he was joined on stage by surprise guest Daniel Stern for a sparkling night of humor and em