In the config_defaults_inc.php, you can now set the ldap real name field. The comment of the field is wrong :

    /**
     * The LDAP field for real name (i.e. common name).
     *  @global string $g_ldap_uid_field
     */
    $g_ldap_realname_field  = 'cn';

It should be :

    /**
     * The LDAP field for real name (i.e. common name).
     *  @global string $g_ldap_realname_field
     */
    $g_ldap_realname_field  = 'cn';