Support root master zone in LDAP; Follow BIND semantics for forwarders.
    
    In this case "support" actually means "remove hack" enforced by mixing
    forward/master zones in one object class.
    
    From now on, forwarding configured in LDAP (attributes idnsForward and
    idnsForwarders) fully follows BIND behavior for master and forward zones:
    
    - Master zones in LDAP are defined by idnsZone object class.
    - Forward zones in LDAP are defined by idnsForward object class.
    
    I.e. idnsForwarders attribute in master zone *does not* change zone type
    to forward.
    
    *THIS IS INCOMPATIBLE CHANGE*
    
    https://fedorahosted.org/bind-dyndb-ldap/ticket/122
    
    Signed-off-by: Petr Spacek <pspacek@redhat.com>