title: Value of UIBackgroundTaskInvalid is?
body: <p>I read from the header file (UIApplication.h):</p>
  
  <pre><code>typedef NSUInteger UIBackgroundTaskIdentifier;
  UIKIT_EXTERN const UIBackgroundTaskIdentifier UIBackgroundTaskInvalid  __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_4_0);
  </code></pre>
  
  <p>It seems that UIBackgroundTaskInvalid is just an ordinary NSUInteger with a given value. Now that I'm writing code that has to be compatible with jailbreaking iOS 3.1.3 (where UIBackgroundTaskInvalid is not defined yet). I might need the real value behind it. Anyone can help?</p>
  
  <p>Thanks in advance.</p>
  
  <p>Di</p>