A.I.G.’s headquarters, that is.  Preservatationists have written to the New York City Landmarks Preservation Commission asking that American International Group’s Art Deco tower on 70 Pine Street in lower Manhattan be designated a city landmark, the New York Post reports.   A.I.G. is trying to sell the tower, as well as a connecting building at 72 Wall Street, and the preservationists are worried that a new owner may ruin the period details that make the building so distinctive.