title: Xcode 4.2 Warnings when dropping Nav Controller on Tab Bar in IB
body: <p>I'm developing an app which is iOS 4 compatible, so my deployment target is set to iOS 4.0.</p>
  
  <p>Whenever I drop a <code>UINavigationController</code> onto a <code>UITabBar</code>, I get these two warnings:   </p>
  
  <ol>
  <li><code>warning: Attribute Unavailable: Defines Presentation Context is not available prior to Xcode 4.2.</code></li>
  <li><code>warning: Attribute Unavailable: Defines Presentation Context on iOS versions prior to 5.0.</code></li>
  </ol>
  
  <p>The <code>UINavigationController</code> functions as expected, in fact, the entire app runs perfectly. But these two warnings are driving me nuts!  </p>
  
  <p>Also, the moment I delete the <code>UINavigationController</code> the warnings disappear.</p>