title: how to make the position of a subclassed UINavigationController overlapped status bar
body: <p>I have a subclass called SubNav which inherits from UINavigationController.
  When I make it like:</p>
  
  <pre><code>window.rootViewController = subNav
  </code></pre>
  
  <p>it shows the NavigationBar at the below of status bar. But in fact I want make its position at the 0,0. not under the status bar 0,20.</p>
  
  <p>But mostly ios7-designed apps in the App Store I saw ,those UINavigationBar is under the status bar.</p>
  
  <pre><code>SubNav : UINavigationController
  </code></pre>
  
  <p>I'm sorry with my poor English,but I'm confusing with it for several days.</p>