PARIS, Oct 19 (Reuters) - France's worst bout of civil unrest in years has plunged President Emmanuel Macron's final months in office deeper into turmoil, exposing the powerlessness of a leader struggling to contain social anger with little money to spend, scant political capital and an increasingly fragile grip on public order. The rioting that swept across France on Saturday, leaving a trail of looted shops, torched buildings and defaced public institutions, presents Macron with perhaps the most explosive challenge of his twilight presidency: a country demanding more from a state that can no longer afford to give much.