[js] don't add __class__ to Array.prototype (closes #2060, closes #1909)

See related issues (#2060, #1909). This fix will make haxe not add `__class__` to `Array.prototype` and check for Array case as it were special in the reflection api. It should impove interoperability with buggy(?) extern js libraries that use `for (var index in array)` for array iteration. It should work even better when/if #2543 is merged.

```haxe
class Main
{
    static function main()
    {
        var a = [1, 2, 3];

        Std.is(a, Array);

        untyped __js__("for (var i in a) {
            console.log(i);
        }");
    }
}
```

Before
```
0
1
2
__class__
```

After
```
0
1
2
```