SOLR-5681: Fixing CHANGES.txt entry

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1597150 13f79535-47bb-0310-9956-ffa450edef68
Move SOLR-5468 to new features section

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1597157 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5681: Fixing CHANGES.txt entry, moving it into the Optimizations section

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1597161 13f79535-47bb-0310-9956-ffa450edef68