title: Rails 3 file_store caching, delete expired fragments
body: <p>I have a Rails 3.2.11 application running on Unicorn and is set up for file_store caching to a specific folder outside of the project.
  I am also using the gem <a href="https://github.com/rails/cache_digests" rel="noreferrer">rails/cache_digests</a> for automatic expiration.
  In a certain page I'm doing fragment caching without setting time expiration.</p>
  
  <p>When a fragment has expired, I see the new fragment created in the cache folder, but I also see the expired fragment as well. How it will be deleted from the cache folder by the cache management mechanism without doing it manually? If it doesn't get deleted then the cache folder will be bloated with garbage, expired fragments that are not used.</p>