SOLR-6342: build.xml clones lucene/CHANGES.txt as LUCENE_CHANGES.txt in solr releases; changes2html hotlinks LUCENE_CHANGES.txt when found

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1618281 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5850: Remove useless checks and properties

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1618282 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5868: fixing botched changes.txt placement/merge from 4.9

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1618285 13f79535-47bb-0310-9956-ffa450edef68