SOLR-4555: When forceNew is used with CachingDirectoryFactory#get, the old CachValue should give up it's path as it will be used by a new Directory instance. 

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_2@1458053 13f79535-47bb-0310-9956-ffa450edef68