SOLR-4624: CachingDirectoryFactory does not need to support forceNew any longer and it appears to be causing a missing close directory bug. forceNew is no longer respected and will be removed in 4.3.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_2@1459568 13f79535-47bb-0310-9956-ffa450edef68