title: Determine if a ruby script is already running
body: <p>Is there an easy way to tell if a ruby script is already running and then handle it appropriately?  For example:  I have a script called really_long_script.rb.  I have it cronned to run every 5 minutes.  When it runs, I want to see if the previous run is still running and then stop the execution of the second script.  Any ideas?</p>