OPENDJ-1585 Add CompactDn class as compact representation of a DN

Rename DN.toNormalizedString() to DN.toIrreversibleNormalizedByteString()


git-svn-id: https://svn.forgerock.org/opendj/trunk/opendj@11207 41b1ffd8-f28e-4786-ab96-9950f0a78031