title: Issue Xcode change char "@" to "%40"
body: <p>I've use the AFNetworking in my app. </p>
  
  <p>When I'll use the AFN with field EMAIL appear this error:</p>
  
  <pre><code>Error: Error Domain=AFNetworkingErrorDomain Code=-1011 "Request failed: not found (404)" UserInfo=0x1096634a0 {NSLocalizedDescription=Request failed: not found (404), NSErrorFailingURLKey=http://mywebservice/vlemail?email=me%40domain.com, AFNetworkingOperationFailingURLResponseErrorKey=&lt;NSHTTPURLResponse: 0x109558d10&gt; { URL: http://mywebservice/vlemail?email=me%40domain.com } { status code: 404, headers {
      Connection = "keep-alive";
      "Content-Length" = 967;
      "Content-Type" = "text/html;charset=utf-8";
      Date = "Mon, 28 Apr 2014 19:01:43 GMT";
      Server = "nginx admin";
  } }, NSUnderlyingError=0x1096756e0 "Request failed: unacceptable content-type: text/html"}
  </code></pre>
  
  <p>It's weird, because the field EMAIL is: 
  NSLog(@" txtEmail.: %@",_txtEmail.text) = [2908:60b]  txtEmail.: me@domain</p>
  
  <p>But in the params of the AFN is changed to: me%40domain</p>
  
  <p>Somebody knows why?</p>
  
  <p>Thanks a lot!</p>