fix several schema checking issues; add rename specific statement for entry...

fix several schema checking issues; add rename specific statement for entry renaming without losing ID (helps e.g. in renaming referrals, otherwise referential integrity would prevent del/add because of referenced stuff in ldap_referrals and ldap_entry_objclasses); referrals need schemacheck off otherwise objectClass chain is invalid (they need to be attached to another objectClass by now; will address this later)