title: Rails detect changes to files programatically
body: <p>I would like to write a method that programatically detects whether any of the files in my rails app have been changed.  Is it possible do do something like an MD5 of the whole app and store that in a session variable?</p>
  
  <p><strong>This is mostly for having some fun</strong> with cache manifest.  I already have a dynamically generated cache and it works well in production.  But in my dev environment,   I would like the id of that cache to update whenever I change anything in the app directory (as opposed to every 10 seconds, which is how I have it setup right now). </p>
  
  <p><strong>Update</strong></p>
  
  <p>File.ctime(".") would be perfect, except that "." is not marked as having changed when deeper directory files have changed.</p>
  
  <p>Does it make sense to iterate through all directories in "." and add together the ctimes for each?</p>