title: UICollectionViewDelegateFlowLayout methods not called on rotation
body: <p>Inside of my Collection View Layout (a subclass of <code>UICollectionViewFlowLayout</code>) I have defined:</p>
  
  <pre><code>- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
      return YES;
  }
  </code></pre>
  
  <p>My expectation is that since rotation is a bounds change, my layout will get recalculated. However when I set a breakpoint in:</p>
  
  <pre><code>- (CGSize)collectionView:(UICollectionView *)collectionView
                    layout:(UICollectionViewLayout *)collectionViewLayout
    sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
  </code></pre>
  
  <p>The breakpoint is not triggered when the screen rotates. Does anyone know why?</p>