LUCENE-5262: StandardDirectoryReader should decRef readers on exception, not close them

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1530051 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5226: add lucene index heap usage to the solr admin UI

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1530169 13f79535-47bb-0310-9956-ffa450edef68