SOLR-6136: Fix spin lock in blockUntilFinished (which eats CPU unnecessarily) using wait/notify and add a unit test for ConcurrentUpdateSolrServer

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1610864 13f79535-47bb-0310-9956-ffa450edef68
(cherry picked from commit 4b9819a93fcf570703d6e06c9b27762d3d0eef4c)

Conflicts:
	solr/CHANGES.txt
	solr/solrj/src/java/org/apache/solr/client/solrj/impl/ConcurrentUpdateSolrServer.java

Resolved CUSS conflicts with previously committed SOLR-4470 (HTTP auth) by keeping the SOLR-4470 changes.
SOLR-6136: backport fixes for precommit issues

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1610908 13f79535-47bb-0310-9956-ffa450edef68
(cherry picked from commit a857460144f106d3c5f511decb99a9742cdde85b)
SOLR-6259: Reduce CPU usage by avoiding repeated costly calls to Document.getField inside DocumentBuilder.toDocument for use-cases with large number of fields and copyFields

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1611853 13f79535-47bb-0310-9956-ffa450edef68
(cherry picked from commit d1acfbda82f0f4c941bedcc12c5de3f77fb62fb8)

Conflicts:
	solr/CHANGES.txt
FOCUS-5337: add field value source that can parse the serialized string value as a float, for use with the LWS click_val field, e.g. 'float(click_val)'