WHEN Reed Birney’s big break finally came, after 30 years as a journeyman actor in New York, he nearly let it pass him by. Like many performers who had seen dream role after dream role go to bigger stars, Mr. Birney had lost faith in himself. Supporting parts and forgettable guests spots on “Law & Order” were cold comfort as he watched, at home in pajamas, as former classmates like Sigourney Weaver and Mercedes Ruehl walked Hollywood red carpets. Mr. Birney even started to believe what an anonymous poster once wrote on a blog about his performances in countless nice-guy parts. That he was a lightweight.