title: What's the correct way to use the CasperJS userAgent function?
body: <p>Not sure what I'm doing wrong here...</p>
  
  <p>My code:</p>
  
  <pre><code>var casper = require('casper').create({
      verbose: true,
      stepTimeout: 10000,
      onError: function() {
          this.captureSelector('error.png', 'html');
      },
      logLevel: "debug"
  });
  
  casper.start();
  
  casper.userAgent('Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)');
  
  casper.setHttpAuth('user', 'pass');
  
  casper.thenOpen('https://www.google.com');
  
  casper.then(function() {
      this.echo(this.getCurrentUrl());
      currentPage = this.getTitle();
      this.captureSelector(currentPage + '.png', 'html');
  });                                
  
  casper.run();
  </code></pre>
  
  <p>My error:</p>
  
  <pre><code>$ casperjs test.js
  [info] [phantom] Starting...
  FAIL TypeError: 'undefined' is not a function (evaluating 'casper.userAgent('Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)')')
  #    type: uncaughtError
  #    error: "TypeError: 'undefined' is not a function (evaluating 'casper.userAgent('Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)')')"
  TypeError: 'undefined' is not a function (evaluating 'casper.userAgent('Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)')')
  </code></pre>