added orderExpr
refactored/improved ParentObj; storing null parent objects to avoid extra queries
added rawOrder
moving object cache to connection level - adding ObjConn, ObjTask, results list,
added an object cache to avoid duplicating parent objects
made ParentObj mutable; using setEntity instead of creating new object
parent record with all null values (left join with no match) should be left null
added REUSE_STMT flag and related arg