title: Reference to property in closure requires explicit 'self.' to make capture semantics explicit
body: <p>Trying to load HTML from a web service into a webview, I get this error:  </p>
  
  <blockquote>
    <p>Reference to property 'webviewHTML' in closure requires explicit 'self.' to make capture semantics explicit</p>
  </blockquote>
  
  <p>What does it mean, and how can I load the HTML string into my web view?</p>
  
  <pre><code>func post(url: String, params: String) {
  
      let url = NSURL(string: url)
      let params = String(params);
      let request = NSMutableURLRequest(URL: url!);
      request.HTTPMethod = "POST"
      request.HTTPBody = params.dataUsingEncoding(NSUTF8StringEncoding)
  
      let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
          data, response, error in
  
          if error != nil {
              print("error=\(error)")
              return
          }
  
          var responseString : NSString!;
          responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
          webviewHTML.loadHTMLString(String(responseString), baseURL: nil)
      }
      task.resume();
  }
  </code></pre>