Code shift, similar to that of r5443.
Shifted the spin number check (cannot have 2 spin with the same number) and 1st element replacement (if that SpinContainer is empty) code from generic_fns.spin.create() to the relax data storage object SpinContainer.add_item() method.
Authored by: bugman 2008-04-08
Parent: [r5444]
Child: [r5446]
