SOLR-6002: CLOSE_LOCK does not need to be static, waitForMerges when DirectUpdateHandler2 closes the IndexWriter, add Greg to CHANGES entry.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1589328 13f79535-47bb-0310-9956-ffa450edef68