A tipster alerted Grub Street yesterday with news that Portofino, which has been slinging Italian at 12th and Walnut streets since Nixon was in office, was closed and the doors and windows were papered over. Was it closed for good? Is another restaurant in the works behind that brown paper barrier? It turns out that the answer to both questions is no. A call to the restaurant revealed that it’s closed for renovations and the staff is on vacation. It should be back in operation by the end of the month.