Federal prosecutors will advocate convicted serial killer James “Whitey” Bulger spend the rest of his life behind bars — plus a symbolic five years after that for good measure — when the sentencing portion of his blockbuster trial gets underway Wednesday.U.S. District Court Judge Denise J. Casper has set aside two days for the event, largely because of the large number of victims’ family members hoping for the chance to address the court about their decades of pain and suffering.