title: topLayoutGuide messes up after UITableViewCell reuse
body: <p>I have a <code>UITableViewCell</code> subclass in which I instantiate a <code>UIViewController</code> subclass and add it's <code>view</code> to the <code>UITableViewCell</code>'s <code>contentView</code>:</p>
  
  <pre><code>viewController.view.frame = CGRectMake(0, 0, contentView.frame.size.width, contentView.frame.size.height)
  contentView.addSubview(viewController.view)
  </code></pre>
  
  <p>Inside <code>viewController</code> (which is created as in a Storyboard), I have a <code>UIImageView</code> which is pinned to the top of the view (well, it's <code>topLayoutGuide</code>, since Xcode 6 Interface Builder seems to only allow me to pin to the <code>topLayoutGuide</code>, and not the container top edge anymore...)</p>
  
  <p>I should also mention that the cell height is 230, which is the same size as <code>viewController.view</code> in Storyboard, so the <code>viewController</code> should take up the entire size of the cell.</p>
  
  <p>This all works fine the first time the cell is displayed, but after reuse the <code>topLayoutGuide</code> in <code>viewController</code> seems to randomly mess up, causing the <code>UIImageView</code> no longer to be pinned to the top of the cell, and is instead shifted down:</p>
  
  <p><strong>On the first display, <code>topLayoutGuide.length</code> is 0 which is correct. However, after scrolling up &amp; down a bit, I can see in the cell's <code>prepareForReuse()</code> that <code>viewController.topLayoutGuide.length</code> changes to 179.333333333333 or 163.666666666667 which causes the whole cell layout to mess up.</strong></p>
  
  <p>I can't figure out why <code>topLayoutGuide</code> is changing itself like this after cell reuse.</p>
  
  <p>I suppose one workaround would be simply to pin the affected <code>UIImageView</code> to the top container edge rather than <code>topLayoutGuide</code>, which would sidestep this issue -- but it seems Xcode 6 no longer provides this functionality (at least, not without creating the constraints manually in code...)</p>
  
  <p>This behaviour is exhibited in iOS 8, I've not tested other iOS versions.</p>