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 is generally done using an EJSVAL_IS_$SOMETHING check which checks if it's an object and if specops are proper.  So in this case we'd use EJSVAL_IS_ARRAYITERATOR.

so here we'd have:

```c
if (!EJSVAL_IS_ARRAYITERATOR(O))
    _ejs_throw_nativeerror_utf8 (EJS_TYPE_ERROR, ".next called on non-ArrayIterator instance");
EJSArrayIterator *OObj = (EJSArrayIterator*)EJSVAL_TO_OBJECT(O);
```