title: UICollectionView + iOS 7 / Xcode 5 = Assertion Failure
body: <p>In my app there was a UICollectionView using flowLayout and it was working beautifully in iOS 6 but fails horribly in iOS 7.  As soon as I segue to the view containing my UICollectionView here's what happens:</p>
  
  <pre><code>*** Assertion failure in -[UICollectionView _createPreparedSupplementaryViewForElementOfKind:atIndexPath:withLayoutAttributes:applyAttributes:], /SourceCache/UIKit/UIKit-2903.2/UICollectionView.m:1401
  *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'the view returned from -collectionView:viewForSupplementaryElementOfKind:atIndexPath
  (UICollectionElementKindSectionHeader,&lt;NSIndexPath: 0x145f3f50&gt; {length = 2, path = 0 - 0}) was not retrieved by calling -dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath: or is nil'
  (&lt;UICollectionReusableView: 0x145f9400; frame = (0 0; 320 20); layer = &lt;CALayer: 0x145f90c0&gt;&gt;)
  </code></pre>