SOLR-5291: Solrj does not propagate the root cause to the user for many errors.
SOLR-3530: Better error messages / Content-Type validation in SolrJ.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1527554 13f79535-47bb-0310-9956-ffa450edef68