Merged revision(s) 1584213 from lucene/dev/trunk:
SOLR-5951: Fixed SolrDispatchFilter to throw useful exception on startup if SLF4j logging jars are missing

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1584214 13f79535-47bb-0310-9956-ffa450edef68