Make invalid 'member' detection work again.

This defines a rootdn globally, and due to OpenLDAP bugs, gives it
manage access to the whole database.  This makes the memberOf module
able to validate the links again, now we have database ACLs.

Andrew Bartlett
(This used to be commit 9fe3e9f09f89fd92f8a16768e53391ff5f8489ec)