Description:
------------
When invoking var_export on an ArrayObject instance it doesn't show 
the numeric indices.

Reproduce code:
---------------
$ao = new ArrayObject(array (2 => "foo", "bar" => "baz"));
var_export ($ao);

Expected result:
----------------
ArrayObject::__set_state(array(
   2 => 'foo',
   'bar' => 'baz',
))

Actual result:
--------------
ArrayObject::__set_state(array(
   'bar' => 'baz',
))