Added Encodable and Decodable for Arc<T>.

[ghost]

No description provided.

[reem]

I'm not sure what the added utility of these methods is; can't you just call .encode if the underlying data is Encodable and just do Arc::new(Decodable::decode(data)) to get Arc<D> where D: Decodable<...>?

[ghost]

@reem it allows #[deriving(Encodable, Decodable)] to work if the structure has an Arc pointer embedded inside of it. Same reason Rc<T> and Box<T> support it.

eg:

#[deriving(Encodable, Decodable)]
struct foo {
    bar: Arc<uint>
}