Allow interface default toString implementation

[Zhong Yu]

On Tue, Jun 10, 2014 at 5:43 PM, Brandon Mintern <mintern at everlaw.com> wrote:

> public class Object implements Objects {

`Object` is supposed to be the root type of everything. It's too odd
if it has a super type.

Even if we do want to allow `toString()` default impl on interfaces,
it'll be much easier to simply special-case it, instead of going
through this exercise.

However, the crux of the matter, I think, is to avoid depending on `toString()`.

Zhong Yu