LUCENE-5780: Make OrdinalMap more memory-efficient.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1604157 13f79535-47bb-0310-9956-ffa450edef68
Fix CHANGES entry formatting.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1604159 13f79535-47bb-0310-9956-ffa450edef68