SOLR-4597: Additional work.

SOLR-4598: The Core Admin unload command's option 'deleteDataDir', should use the DirectoryFactory API to remove the data dir. 

SOLR-4599: CachingDirectoryFactory calls close(Directory) on forceNew if the Directory has a refCnt of 0, but it should call closeDirectory(CacheValueValue).

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1457556 13f79535-47bb-0310-9956-ffa450edef68