LUCENE-5449: Rename _TestUtil to TestUtil.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1569597 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5449: _TestHelper -> TestHelper.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1569598 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5449: add CHANGES.txt.

This closes #36.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1569599 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5620: ZKStateReader.aliases should be volatile to ensure all threads see the latest aliases.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1569603 13f79535-47bb-0310-9956-ffa450edef68