Hotfix for servers with directory listings / web accessible w3tc database cache directories

git-svn-id: http://plugins.svn.wordpress.org/w3-total-cache/trunk@645436 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fixed security issue that can occur if using database caching to disk. If using database caching to disk with a web server with directory listing or web accessible wp-content/w3tc/dbcache/* directories. This patch works for all hosting environments / types where PHP is properly configured, i.e. .htaccess modifications (or other web server configuration changes) are *not* necessary to ensure proper security.

git-svn-id: http://plugins.svn.wordpress.org/w3-total-cache/trunk@645743 b8457f37-d9ea-0310-8a92-e5e31aec5664