ldap.h claims to support draft-ietf-ldapext-ldap-c-api-04.txt and not draft-ietf-ldapext-ldap-c-api-05.txt , the last version of the draft.
As 2.x moves forward, I think we should aim for compatibility with our existing implementation (of a LDAPext LDAP C API I-D). Those who want RFC 1823/U-Mich LDAP compatibility should use OpenLDAP 1.x.
--Kervin