Allow usage of select expressions in order by, even with group by/distinct.

We currently do not allow order by keys to reference anything other select aliases if a simple query uses distinct or group by. We could allow for the projected expressions to resolve as well.

For example:
select x as y from t group by x order by x
instead of order by y

Mondrian generates queries of this form, although I'm not sure if that's something that could be customized through Mondrian.