LUCENE-6074: symlink jars on unix/os X systems

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1641236 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-6068: LeafReader.fields never returns null

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1641239 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-6070: Fix forbidden-apis and deprecations of Java 8 when used with Java 9

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1641302 13f79535-47bb-0310-9956-ffa450edef68