Ticket #47692 single valued attribute replicated ADD does not work

https://fedorahosted.org/389/ticket/47692
Reviewed by: nhosoi,lkrispenz (Thanks!)
Branch: 389-ds-base-1.3.0
Fix Description: Add special corner case handling for the case where
- attr is deleted with vdcsn and adcsn CSN1
- attr vucsn is NULL
- incoming mod/add has CSN2 where CSN2 > CSN1
in this case, just keep the new mod/add value as the present value.
Platforms tested: RHEL6 x86_64
Flag Day: no
Doc impact: no
(cherry picked from commit 59941ea23b6f288617ba1e6ce58238fa59266c9f)
(cherry picked from commit 01a112121e80505021d0a18afa899b5c46180797)
(cherry picked from commit a4a46424d59a189552c1d17eed1d52218f3a95b8)