LUCENE-4859: Expose more stats on IndexReader

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1458914 13f79535-47bb-0310-9956-ffa450edef68
SOLR-4589: Fixed CPU spikes and poor performance in lazy field loading of multivalued fields (merge r1458887)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1458938 13f79535-47bb-0310-9956-ffa450edef68