for t in new_tree.iter() {
                debug!("t = {:?}", t.name());
                if let Some(n) = t.name() {
                    let n = Path::new(n).to_path_buf();
                    prefixes.insert(n);
                }
            }

            use git2::{TreeWalkMode, TreeWalkResult};
            new_tree
                .walk(TreeWalkMode::PreOrder, |x, t| {
                    debug!("t = {:?} {:?}", x, t.name());
                    if let Some(n) = t.name() {
                        let mut m = Path::new(x).to_path_buf();
                        m.push(n);
                        prefixes.insert(m);
                    }
                    TreeWalkResult::Ok
                })
                .unwrap();