title: -systemLayoutSizeFittingSize: returning incorrect height for tableHeaderView under iOS 8
body: <p>There are numerous threads about correctly sizing a tableHeaderView with auto-layout (<a href="https://stackoverflow.com/questions/20982558/how-do-i-set-the-height-of-tableheaderview-uitableview-with-autolayout">one such thread</a>) but they tend to pre-date iOS 8.</p>
  
  <p>I have a situation with numerous table views, all with headers, that size correctly under iOS 7 but incorrectly under iOS 8 using the code that most of the aforementioned threads champion. In the controllers for the tables, I have the following method:</p>
  
  <pre><code>- (void)rejiggerTableHeaderView
  {
      self.tableView.tableHeaderView = nil;
  
      UIView *header = self.headerView;
  
      [header setNeedsLayout];
      [header layoutIfNeeded];
  
      CGFloat height = [header systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
  
      CGRect headerFrame = header.frame;
      headerFrame.size.height = height;
  
      header.frame = headerFrame;
  
      self.tableView.tableHeaderView = header;
  }
  </code></pre>
  
  <p>With a multi-line label under iOS 7, this correctly sizes the table view's header like so:</p>
  
  <p><img src="https://i.imgur.com/FQxFR0s.png" /></p>
  
  <p>But the same code run under iOS 8 produces the following:</p>
  
  <p><img src="https://i.imgur.com/JOXLEsG.png" /></p>
  
  <p>What's the trick to getting -systemLayoutSizeFittingSize: to return the correct size under iOS 8? <a href="https://www.dropbox.com/s/jyi4if92x4zj1c4/IncorrectHeight.zip?dl=0" rel="noreferrer">Here's a sample project</a> that demonstrates the issue.</p>