OSRA273 fix duplicate osra_num on import

OSRA273 fix duplicate osra_num on import
@nik This is necessary because validating the orphan creates a sequential_id which then becomes incorrect if another orphan is validated before the first orphan is saved.

@PurityControl  As the osra_num is based on the seq_id then it is generated from an incorrect value if another unsaved orphan2 has been validated before orphan1 was persisted.  Delaying the generation of the osra_num until save allows us to correct the sequential_id first.  Before_save will not affect the updating of an orphan because once an orphan has been persisted it has its own sequential_id, which will generate the same osra_num on recalculation.  Test added to verify this.