r12179: Allow our KDC to use LDAP to get to the backend database.

r12179: Allow our KDC to use LDAP to get to the backend database.

To avoid a circular depenency, it is not allowed to use Krb5 as an
authentication mechanism, so this must be removed from the list.  An
extension to the credentials system allows this function.

Also remove proto.h use for any of the KDC, and use NTSTATUS returns
in more places.

Andrew Bartlett