title: How to use Active Support core extensions
body: <p>I have Active Support 3.0.3 installed and Rails 3.0.3 with Ruby 1.8.7.</p>
  
  <p>When I try to use <code>1.week.ago</code> I get </p>
  
  <pre><code>NoMethodError: undefined method 'week' for 1:Fixnum
  from (irb):2
  </code></pre>
  
  <p>The other core extensions seem to work. I tried it on a friend's computer (same install specs and legacy versions are on his) with the same results.</p>
  
  <p>What gives?</p>
  
  <p>All of this is in IRB.</p>