title: NSURLSession set header 'Connection' to 'Upgrade' not work
body: <p>Environment: Mac OS X 10.9, Xcode 5.0.2</p>
  
  <p>I need to create an HTTP request for my mini WebSocket client, example request:</p>
  
  <pre><code>GET / HTTP/1.1
  Host: serverwebsocket.com:10080
  Upgrade: websocket
  Connection: Upgrade
  Origin: http://from.com
  </code></pre>
  
  <p>I've created <code>NSURLSession</code> with <code>NSURLSessionConfiguration</code> and set the headers, and Wireshark shows all header set except <code>Connection</code> which stays <code>keep-alive</code>, but should not.</p>
  
  <pre><code>// Create request based on Sessions
  
  // Create sesson configuretion
  NSURLSessionConfiguration* sessionConf = [NSURLSessionConfiguration defaultSessionConfiguration];
  
  // Configure session config
  // set header value, detail header websocket on http://learn.javascript.ru/websockets
  sessionConf.HTTPAdditionalHeaders = @{@"Upgrade": @"websocket",
                                        @"Connection": @"Upgrage",
                                        @"Origin": @"http://from.com",
                                        @"User-Agent": @"Chrome/36.0.198.5.143"};
  
  // Declare handler block of response
  __block void (^handler)(NSData* data, NSURLResponse* response, NSError* error);
  
  handler = ^(NSData* data, NSURLResponse* response, NSError* error)
  {
      // If receive response from server
      if(data)
      {
          NSString* result = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
          NSLog(@"response data: %@", result);
  
      }
      else // something wrong
      {
          NSString* errorText;
  
          if(error)
          {
              errorText = [error localizedDescription];
          }
          else // Generic description
          {
              errorText = @"Error Interner connection";
          }
          NSLog(@"Request error: %@",errorText );
      }
  };
  
  
  // Create Session
  NSURLSession* session = [NSURLSession sessionWithConfiguration:sessionConf];
  
  NSURL* url = [NSURL URLWithString: [_textUrl stringValue]];
  
  [[session dataTaskWithURL:url completionHandler:handler] resume];
  </code></pre>
  
  <p>How can I change the header for <code>Connection</code>? And I do not want use another websocket library, I want to handle HTTP header in low level.</p>
  
  <p>May, instead of the <strong>NSURLSession</strong> there are other classes work with network? In <strong>NSURLRequest</strong> same problem.</p>