SOLR-2417, updating CHANGES.txt to show the explain syntax that was added in SOLR-1566
SOLR-2417, updating CHANGES.txt to show the explain syntax that was added in SOLR-1566

git-svn-id: 308d55f399f3bd9aa0560a10e81a003040006c48@1085533 13f79535-47bb-0310-9956-ffa450edef68

apache/solr,apache/solr,apache/solr,apache/solr,apache/solr