SOLR-5428: New 'stats.calcdistinct' parameter in StatsComponent returns set of distinct values and their count. This can also be specified per field e.g. 'f.field.stats.calcdistinct'

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1544044 13f79535-47bb-0310-9956-ffa450edef68