LUCENE-5969: javadocs

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1629406 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5969: add changes and test

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5969@1629408 13f79535-47bb-0310-9956-ffa450edef68