SOLR-1301: Throw an error if HdfsDirectoryFactory is not configured for now.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1558671 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5636: SolrRequestParsers does some xpath lookups on every request, which can cause concurrency issues.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1558690 13f79535-47bb-0310-9956-ffa450edef68