old_contents: var Scanner = require('./url-scanner'),
      url = require('./url');
  
  function mergeUrls() {
    new Scanner(this.root, this.imagesSeen).combine();
    return new nodes.Expression(false);
  }
  
  module.exports = function(options) {
    return function(stylus) {
      stylus.define('url', url(options));
      stylus.define('merge-urls', mergeUrls);
    };
  };
  
new_contents: var Scanner = require('./url-scanner'),
      url = require('./url'),
      stylus = require('stylus'),
        nodes = stylus.nodes;
  
  function mergeUrls() {
    new Scanner(this.root, this.imagesSeen).combine();
    return new nodes.Expression(false);
  }
  
  module.exports = function(options) {
    return function(stylus) {
      stylus.define('url', url(options));
      stylus.define('merge-urls', mergeUrls);
    };
  };
  
subject: Fix missing var reference.