title: Rails 3/Cucumber problem: "...already activated builder 3.0.0, but your Gemfile requires builder 2.1.2"
body: <p>I've been using cucumber without trouble for with Rails 3 for a while, but after a whole bunch of tinkering today (including gem cleanup), I get the following error whenever I run "cucumber features"</p>
  
  <blockquote>
    <p>You have already activated builder
    3.0.0, but your Gemfile requires builder 2.1.2. Consider using bundle
    exec. (Gem::LoadError)</p>
  </blockquote>
  
  <p>Tried it in multiple rails projects on my machine - all are effected. Not quite sure how to tackle this one - tried installing 2.1.2 &amp; specifying it in the gemfile, but no joy.</p>
  
  <p>"bundle exec cucumber features" does work, but it doesn't seem to play nicely with autotest.</p>
  
  <p>Any suggestions regarding what I've done (and better still how to fix it) much appreciated.</p>