[WIP] Adding a test exhibiting issue with SessionStorage

These tests show that the SessionStorage implementation is not compatible with 3rd party PHP libraries that manipulate the $_SESSION directly. If the library tries to unset a multi-dimensional session array, a Notice is thrown and the item is not unset:

```
$storage = new \Zend\Session\Storage\SessionStorage();
$_SESSION['foo']['bar'] = 'baz';
unset($_SESSION['foo']['bar']);
\Zend\Debug\Debug::dump($_SESSION);

/* OUTPUT

Notice: Indirect modification of overloaded element of Zend\Session\Storage\SessionStorage has no effect in /Users/ncalugar/Zend/workspaces/DefaultWorkspace/phantom/public/index.php on line 16

object(Zend\Session\Storage\SessionStorage)#2 (2) {
  ["isImmutable":protected] => bool(false)
  ["storage":"ArrayObject":private] => array(2) {
    ["__ZF"] => array(1) {
      ["_REQUEST_ACCESS_TIME"] => float(1356130641.3591)
    }
    ["foo"] => array(1) {
      ["bar"] => string(3) "baz"
    }
  }
}
*/
```
This seems to be related to: https://bugs.php.net/bug.php?id=52861