(Reuters) -An accused former street gang leader was arrested on Friday on a charge of murder in the Las Vegas shooting death of hip-hop star Tupac Shakur nearly three decades ago, marking a breakthrough for a long-unsolved case that was a defining moment in the history of rap music. A grand jury in Clark County, Nevada, returned an indictment charging Duane "Keffe D" Davis with one count of murder with a deadly weapon for his alleged role in leading a group of men to kill Shakur in a 1996 drive-