title: deleted migration file keeps coming back Rails 3
body: <p>I have 2 versions of the same migration (bad habit, I know). I deleted old version many times, but after restarting my project (or do something with it, like rake db:test:prepare), the file shows up in my migrate folder. When I run rake db:migrate, it will complain about multiple migrations with the same name.</p>
  
  <p>How can I delete a migration file completely? Is there a registry that I need to remove to prevent it from coming back?</p>