Comedian Jerry Seinfeld has stepped into the director’s shoes for his new film “Unfrosted,” the not-quite-true story of the creation of the Kellogg’s Pop-Tart. Correspondent Mo Rocca talks with Seinfeld about working behind the camera for the first time, and calling on a bunch of his comedian friends (including “Sunday Morning” contributor Jim Gaffigan) to act in his origin tale of a breakfast staple.