title: support iOS 5.1 NSURLIsExcludedFromBackupKey [do not backup] without Lion installed?
body: <p>I see it's apparently possible to <a href="https://stackoverflow.com/questions/8376127/ios-submission-without-lion">submit apps without Lion installed</a>, but my app downloads some large files, which need to be saved according to <a href="https://developer.apple.com/library/ios/#qa/qa1719/_index.html" rel="nofollow noreferrer">Apple storage guidelines</a>.</p>
  
  <p>Including the code below, I can't even compile due to <code>Use of undeclared identifier 'NSURLIsExcludedFromBackupKey'</code>:</p>
  
  <pre><code>-(BOOL)addSkipBackupAttributeToItemAtURL:(NSURL *)URL{
      if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"5.1")) {
          assert([[NSFileManager defaultManager] fileExistsAtPath: [URL path]]);
  
          NSError *error = nil;
          BOOL success = [URL setResourceValue: [NSNumber numberWithBool: YES]
                                        forKey: NSURLIsExcludedFromBackupKey error: &amp;error];
          if(!success){
              NSLog(@"Error excluding %@ from backup %@", [URL lastPathComponent], error);
          }
          return success;
      }
  }
  </code></pre>
  
  <p>How can I keep using this code while I've only got iOS 5.0 SDK in xcode?</p>
  
  <p>(or is my desire moot because I literally cannot tell my app it supports iOS 5.1?)</p>
  
  <ul>
  <li>(<code>SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO</code> comes from <a href="https://stackoverflow.com/a/5337804/194309">https://stackoverflow.com/a/5337804/194309</a>)</li>
  </ul>