Support subselects in ON clause if join type is FULL OUTER

[terrajobst]

Ported from CodePlex

Currently, NQuery does not support subqueries in an ON clause of a join if the join type is FULL OUTER (throws InternalError). For example, the following query cannot be executed:

SELECT  *
FROM    Territories t
            FULL JOIN EmployeeTerritories et ON et.TerritoryID = t.TerritoryID AND
                        EXISTS (
                            SELECT  *
                            FROM    Territories it
                            WHERE   it.TerritoryId = et.TerritoryId
                        )

[dallmair]

Works fine in v.Next (results also look good to me).