BOSTON (AP) — Behind the convictions of Boston's most powerful mobsters over the past 30 years, there has been one constant: federal prosecutor Fred Wyshak.For the dauntless assistant U.S. attorney, last month's murder conviction of former New England Mafia Boss Francis "Cadillac Frank" Salemme likely closes the book on a lengthy saga that exposed the FBI's overly cozy relationship with its gangster informants and decimated the region's organized-crime underworld."It has [...]