OPENDJ-1342 Migrate AVA, RDN, and DN classes

These changes are required to complete the migration of the server to the SDK's DN and RDN classes.

DN.java:
In toNormalizedByteString(), changed the representation to include a leading NORMALIZED_RDN_SEPARATOR
 when for all DNs other than the root DN.
This is consistent with how the server stores data in dn2id or dn2uri.
Moved RDN.AVA_CHAR_SEPARATOR here, to be consistent with NORMALIZED_* constants.
Added RDN_CHAR_SEPARATOR and used it throughout this class.
Added valueOf(ByteString), rdn(int) and toUUID().
Moved hasAttributeType() here from server's RDN.
Inlined static method compareTo(DN, DN)

RDN.java:
Added MIN_VALUE and minValue(), and modified code to take care of it.
Moved AVA_CHAR_SEPARATOR to DN class and used it throughout this class.

DNTestCase.java:
Added test cases for using RDN.maxValue() and DN.minValue() with a Map keyed by DNs

DistinguishedNameEqualityMatchingRuleTest.java:
Consequence of the change to DN.toNormalizedByteString()