Thanks to Rich for the good idea to enhance the procedure.
> What if we do what replication conflicts do and rename the entry to
> nsuniqueid=<uuid>+oldDN?  or use some other unique name?

Based upon the suggestion by Rich, in case duplicated DNs are found, the second
DN is renamed to nsuniqueid=<uuid>+oldDN (import_foreman in import-threads.c).

In addition, there was a bug to handle multi-valued RDNs in
slapi_dn_normalize_ext.  In case multi-valued RDN appears with DN value (e.g.,
it was not normalized properly.  Introduced additional rdn_av_stack
(subinitial_rdn_av_stack) for the nested DN value.