SOLR-5636: Move CHANGES entry to 4.6 branch

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1559584 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5577: Harden leaking Timer thread.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1559588 13f79535-47bb-0310-9956-ffa450edef68