title: Casperjs/Phantomjs Modifying headers
body: <p>i'm trying to change some headers but nothing is working:</p>
  
  <pre><code>var casper = require('casper').create({ // 
      stepTimeout: 15000, 
      verbose: false, 
      logLevel: 'error', 
      pageSettings: { 
          loadImages: true, 
          loadPlugins: true, 
          userAgent: 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.364',
          customHeaders: { 
              Connection: 'keep-alive', 
              Accept: 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8' 
  } } });
  </code></pre>
  
  <p>I also tried:</p>
  
  <pre><code>phantom.page.customHeaders = { 
      "User-Agent" : "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:26.0) Gecko/20100101 Firefox/26.0", 
      "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8", 
      "Accept-Language": "en-US,en;q=0.5", "Accept-Encoding": "gzip, deflate",
      "Connection" : "keep-alive" };
  </code></pre>
  
  <p>And for a single connection:</p>
  
  <pre><code>this.open('http://localhost/post.php', { 
      method: 'post', 
      headers: { 'Accept': 'application/json' } 
  });
  </code></pre>
  
  <p>None of them are working or am i doing something wrong?
  Thanks</p>