message: use top level err handling
diff: @@ -77,7 +77,7 @@ pub fn install(root: Option<&str>,
  match install_one(root, map, Some(krate), source_id, vers, opts, force, first) {
  Ok(()) => succeeded.push(krate),
  Err(e) => {
  - opts.config.shell().error(e)?;
  + ::handle_error(e, &mut opts.config.shell());
  failed.push(krate)
  }
  }
  