NEW YORK (Reuters) - Former New York mayor and presidential hopeful Rudolph Giuliani gained fame for his performance after the September 11 attacks, but charges that he also made serious blunders could give ammunition to rival candidates. Giuliani, a Republican, has all but formally declared his candidacy and polls show he is a strong contender, largely because of his steely and comforting leadership that day in 2001. But Giuliani also made mistakes in handling the city's emergency services that may have cost lives, say the co-authors of the 2006 book "Grand Illusion: The Untold Story of Rudy Giuliani and 9/11."...