Decorator base classes for query related objects

Doctrine\ORM\Query should not be directly extendable but it would be nice to decorate query objects and add additional methods. Use cases are e.g. doctrine-fun (see https://github.com/lstrojny/doctrine-fun/blob/master/src/Doctrine/Fun/Query.php) or even cases where users want to add domain specific methods. As Doctrine\ORM\Query is final it is not so easy to decorate correctly. I would propose:

• Add a new interfaces: Doctrine\ORM\QueryInterface that provides a contract for all methods Doctrine\ORM\Query provides
• Add a decorator base class Doctrine\ORM\QueryDecorator as an extension point
• Some for NativeQuery and QueryBuilder