LUCENE-5939: Regenerate old backcompat indexes to ensure they were built with the exact release

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1624660 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5939: Add changes entry

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1624661 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5930: IntelliJ config: drop resource-only modules, add module groups, and add module for lucene/backward-codecs, and fix up a bunch of other little issues

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1624671 13f79535-47bb-0310-9956-ffa450edef68