…ble.

This fixes the following example case:

```js
$.extend(true, {}, {a:['a']})
```
Prior to this change, the above would trigger maximum call stack error.
This is because the `[]` computed property added to the array prototype
references itself, which ultimately makes `$.extend` (and other deep
equality style comparisons) fail.

Unfortunately, `class Foo extends Array{}` doesn't work well with older
browsers (and would even require changes in our transpilation for
production builds for modern ones).

The actual test doesn't care if its running on an Array (without the
fixes in this PR this modified test still fails the same way).