SOLR-1632: Distributed IDF, finally. (merge from trunk)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1648428 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6448: SolrJ support for all Collection API calls (merge from trunk)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1648447 13f79535-47bb-0310-9956-ffa450edef68