state more fully when queries are derived from
themselves + a selectable (i.e. from_self(),
union(), etc.), so that join() and such have the
correct state to work from.  [ticket:1853]

- Fixed bug where Query.join() would fail if
querying a non-ORM column then joining without
an on clause when a FROM clause is already
present, now raises a checked exception the
same way it does when the clause is not
present.  [ticket:1853]