err=20 when rdn attr name is different that attr name in object (ITS#1997)

[kevin@kogz.com]

Full_Name: Kevin McCarthy
Version: 2.1.3
OS: Linux
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (67.105.66.160)


When the RDN attribute name case differs from the case of the attribute name
inside the object body, err=20 (attribute 'XXX' provided more than once) is
thrown.

Example:

DN: userName=kevin, ou=people, dc=test, dc=com
username: kevin
objectclass: person
...

[LDAP: error code 20 - attribute 'userName' provided more than once]

ldapadd should be smart enough to detect this case and accept the entry,
especially since certain client map all DNs TO UPPER CASE.