The fiend behind Sunday's bloodbath at a packed Austin bar was an ex-New York City resident wearing a "Property of Allah'' hoodie — and possibly out for vengeance over the US attack on Iran, law-enforcement sources told The Post. Crazed Texas shooter Ndiaga Diagne, 53, of Senegal arrived in the US on March 13, 2000 on a B-2 tourist visa during the Democratic Clinton administration and became a lawful permanent resident (IR-6) when he married a US citizen in June 2006, a source familiar with his immigration history told The Post...