Herrrrrre’s Branford: Jay Leno said Thursday it’s all but official: Branford Marsalis will succeed Doc Severinsen as bandleader on “The Tonight Show.” Leno, who takes over for Johnny Carson in May, said the saxophonist “has an incredible knowledge of music. He’s worked with everybody from Sting to classical to jazz. He can play anything. . . . I think he’ll draw other excellent musicians to the program.” Leno added that Marsalis “probably” will compose a new theme for the show. “We’re just going through the motions” now of signing a contract, said Leno. It “looks like it’ll happen once they dot the i’s and all that stuff.” Leno was in Washington promoting a book and speaking at the National Press Club. His stay in the capital included a visit to the White House, where he dropped a barrage of one-liners on the nation’s leaders.