Adds support for alias relabeling permitting excludes and updates for aggregates filtered on remote foreign key relations

Apart from correcting the relabeling of aliases, I've corrected the test for it and added a new one to make a difference between aggregates filtering on m2m relations and ones filtering on remote foreign key relations.

Check it out and give me your thoughts on it.

Thanks for a life-saving extension to the ORM!

Hampus