[GH-485] Back ported changes of SimpleConditionalExpression

This issue is created automatically through a Github pull request on behalf of sstok:

Url: https://github.com/doctrine/doctrine2/pull/485

Message:

This following query fails.

```
SELECT I FROM Rollerworks\Bundle\RecordFilterBundle\Tests\Fixtures\BaseBundle\Entity\ECommerce\ECommerceInvoice I WHERE ((RECORD_FILTER_FIELD_CONVERSION('invoice_customer', I.customer) BETWEEN :invoice_customer_0 AND :invoice_customer_1) AND (RECORD_FILTER_FIELD_CONVERSION('invoice_customer', I.customer) NOT BETWEEN :invoice_customer_2 AND :invoice_customer_3))
```

With this message.
```
[Syntax Error] line 0, col 306: Error: Expected =, <, <=, <>, >, >=, !=, got 'NOT'
```

It only happens in version 2.2, 2.3 is working as expected.

I have traced the fix to one very simple change in SimpleConditionalExpression and only seem to happen when using an custom function NOT and having nested parenthesis.

As far as I can tell its BC.