Italian police on Sunday used new powers for preventative detention on anarchists seeking to take part in an unauthorised protest in Rome.     The police detained 91 people "deemed dangerous" at several different entrances to Rome's Acquedotti Park.     They wanted to take part in a march to commemorate two anarchists killed in an explosion in an abandoned farmhouse in the park on March 19, allegedly while trying to make a bomb.     Premier Giorgia Meloni's government passed a decree making it