Bug 696407 - If an entry with a mixed case RDN is turned to be
    a tombstone, it fails to assemble DN from entryrdn
    
    https://bugzilla.redhat.com/show_bug.cgi?id=696407
    
    Description: When an entry is turned to be a tombstone, the RDN
    part is replaced with this unusual format:
        "nsuniqueid=9a63a581-...-ca8fe9f7,uid=TestUser"
    A helper function slapi_rdn_replace_rdn was introduced to support
    the replace task, in which function, normalized rdn field "nrdn"
    was supposed to have lowered case RDN, but it was not. This patch
    fixes it.