D6632: rust-dirstate: rust implementation of dirstatemap

[Yuya Nishihara]

> +        if let Some(ref mut file_fold_map) = self.file_fold_map {
> +            file_fold_map
> +                .remove::<Vec<u8>>(filename.to_ascii_uppercase().as_ref());

Looks incompatible with the dirstate class, which uses util.normcase().