SOLR-5465: SolrCmdDistributor retry logic has a concurrency race bug. 
SOLR-5464: ConcurrentSolrServer does not stream pure delete by id requests.
SOLR-5452: Do not attempt to proxy internal update requests.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1543300 13f79535-47bb-0310-9956-ffa450edef68