Something to consider is a later commit is that `_.prototype.slice` will still produce sparse arrays. Addressing that with a `slice` helper would allow replacing the `_.toArray` reference in `_.clone` with `slice` and allow replacing all the `Array.prototype.slice.call(...)`  equiv use with the `slice` helper. Besides being consistent it also helps perf as engines currently disqualify functions for certain optimizations if they use/access `arguments` objects outside a narrow happy path.