Initial fun for Array iterator.

We are missing yet:

1. The special key+value return value (which I haven't seen in action anywhere yet, but still documented in the spec)
2. Plugging it into the Array @@iterator call.

I expected to send this request yesterday, but was too tired and forgot ;(

this should be up under 1, and under 2:
```c
if (!EJSVAL_IS_ARRAYITERATOR(O))
    _ejs_throw_nativeerror_utf8 (EJS_TYPE_ERROR, ".next called on non-object");
```