Remove BC break in Identical validator

A BC break was introduced a few days ago in Identical component (https://github.com/zendframework/zf2/commit/fcbe185a24d10a90a17c0907fff02ea14a18a403#library/Zend/Validator/Identical.php).

My use case which was valid was specifying the token as a single value:

```php
$inputFilter->add(array(
            'name'       => 'accept',
            'validators' => array(
                array(
                    'name'    => 'Identical',
                    'options' => array(
                        'token' => '1',
                        'messages' => array(
                            'notSame' => 'Vous devez d\'abord accepter la charte de Capitaine Job !'
                        )
                    )
                )
            )
        ));
```

However this was not accepted anymore because it threw in exception.