message: Implement ControlFlow for Result<C, E> C: ControlFlow instead of just Result<(), E>.
diff: @@ -93,13 +93,13 @@ impl<B> ControlFlow for Control<B> {
  }
  }
  -impl<E> ControlFlow for Result<(), E> {
  - fn continuing() -> Self { Ok(()) }
  +impl<C: ControlFlow, E> ControlFlow for Result<C, E> {
  + fn continuing() -> Self { Ok(C::continuing()) }
  fn should_break(&self) -> bool {
  self.is_err()
  }
  fn should_prune(&self) -> bool {
  - false
  + if let Ok(ref c) = *self { c.should_prune() } else { false }
  }
  }
  