message: Make PackageId derive Copy
diff: @@ -18,7 +18,7 @@ lazy_static! {
  }
  /// Identifier for a specific version of a package in a specific source.
  -#[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
  +#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
  pub struct PackageId {
  inner: &'static PackageIdInner,
  }
  