title: error for setting range for NSURLConnection, NSMutableURLRequest
body: <p>I am trying to implement download resuming functionality by using 
  setValue:forHTTPHeaderField.
  But whenever I use that method, I get an </p>
  
  <blockquote>
    <p>[NSURLRequest setValue:forHTTPHeaderField:]: unrecognized selector
    sent to instance 0x4e0b710 2011-08-08 22:44:36.469 Patch[9140:207] <em>*</em>
    Terminating app due to uncaught exception
    'NSInvalidArgumentException', reason: '-[NSURLRequest
    setValue:forHTTPHeaderField:]: unrecognized selector sent to instance
    0x4e0b710'</p>
  </blockquote>
  
  <p>error.</p>
  
  <p>My code works fine without that method but when I include this code, I get the error above</p>
  
  <pre><code>NSMutableURLRequest* request = [NSURLRequest requestWithURL:[NSURL URLWithString:URL]
                                           cachePolicy:NSURLRequestUseProtocolCachePolicy
                                       timeoutInterval:60.0];
  
  //---------------- setting range for download resume -----------------------
  NSString* range = @"bytes=";
  range = [range stringByAppendingString:[[NSNumber numberWithInt:offset] stringValue]];
  range = [range stringByAppendingString:@"-"];
  NSLog(@"range: %@", range);
  
  [request setValue:range forHTTPHeaderField:@"Range"];
  </code></pre>
  
  <p>please help me... Thank you very much</p>