JDO : Support DISTINCT properly

[Timo Westkämper]

JDOQLQuery query = ...
QCarModel model = QCarModel.carModel;
query.from(model).where ....
return query.listDistinct(model);

Datanucleus generates error : "variable=DISTINCT is not yet bound so returning UnboundExpression"

[Timo Westkämper (timo-westkamper)]

Fixed by always serializing the projection, when distinct is declared :

SELECT DISTINCT FROM parts.beans.CarModel WHERE ...

becomes

SELECT DISTINCT this FROM parts.beans.CarModel WHERE ...

[Timo Westkämper (timo-westkamper)]

Released in 2.2.0-beta4