title: d3 layout is undefined
body: <p>Trying to use <a href="http://mbostock.github.com/d3/" rel="noreferrer">d3.js</a> and not sure how to reference it properly:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;head&gt;
  &lt;link rel="stylesheet" href="bootstrap.min.css"&gt;
  &lt;script src="jquery-1.7.1.js"&gt;&lt;/script&gt;
  &lt;&lt;&lt;&lt;other scripts&gt;&gt;&gt;
  &lt;script src="topbar.js"&gt;&lt;/script&gt;
  &lt;script&gt;
  $(function() {
      var n = 4, // number of layers
          m = 64, // number of samples per layer
       data = d3.layout.stack()(stream_layers(n, m, .1)),
      color = d3.interpolateRgb("#aad", "#556");
  });
  &lt;/script&gt;
  &lt;/head&gt;
  ...
  &lt;/html&gt;
  </code></pre>