- An instance which is moved to "transient", has

- An instance which is moved to "transient", has
an incomplete or missing set of primary key
attributes, and contains expired attributes, will
raise an InvalidRequestError if an expired attribute
is accessed, instead of getting a recursion overflow.

- make_transient() removes all "loader" callables from
the state being made transient, removing any
"expired" state - all unloaded attributes reset back
to undefined, None/empty on access.