CHARLESTON, S.C. — Two things stand out about this week’s indictment of a white former South Carolina police officer on federal civil rights charges in the death of unarmed black motorist Walter Scott: Such charges from the feds against an officer are relatively rare, and they send a message.Michael Slager, 34, already faces state murder charges in Scott’s death.Some, including attorneys for Scott’s family, see the new indictment as a message from federal prosecutors that they’ve got their eye …