- Using a "dynamic" loader with a "secondary" table now produces

- Using a "dynamic" loader with a "secondary" table now produces
a query where the "secondary" table is *not* aliased.  This
allows the secondary Table object to be used in the "order_by"
attribute of the relation(), and also allows it to be used
in filter criterion against the dynamic relation.
[ticket:1531]

- a "dynamic" loader sets up its query criterion at construction
time so that the actual query is returned from non-cloning
accessors like "statement".