title: UICollectionView: different size items is not calculated on reused items
body: <p>I have a collection view with varied item sizes which i declare in </p>
  
  <pre><code>- (CGSize)collectionView:(UICollectionView *)collectionView
                    layout:(UICollectionViewLayout*)collectionViewLayout
    sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
  
      FeedItem *item = [_imagesLinkArray objectAtIndex:indexPath.row];
      return CGSizeMake(250, 200*item.sizeFactor);
  }
  </code></pre>
  
  <p>When the cell is being reused in <code>collectionView:cellForItemAtIndexPath:</code> 
  the item is being rendered with the reuesed item size and not the one specified in <code>sizeForItemAtIndexPath:</code>.</p>
  
  <p>any ideas?</p>