Celtics coach Doc Rivers isn’t quite ready to say Rajon Rondo is in a slump. “He’s not playing great right now, but I don’t think he’s slumping,” Rivers said. Whatever you call it, one thing is clear: Rondo is not playing Rondo-esque basketball. And the Celtics are worse off for it. The latest rough outing for Rondo and the C’s came in Monday’s 88-79 loss to the New Jersey Nets. It was the Celtics’ third loss in their last four games, and now has them dropped them into a tie with Chicago (47-18) for the best record in the Eastern Conference.