title: Does the @@iterate_diff view from plone.app.iterate work with plone.app.stagingbehavior?
body: <p>I have a custom type made using <a href="http://plone.org/products/dexterity/" rel="nofollow">dexterity</a> and <a href="https://github.com/plone/plone.app.stagingbehavior" rel="nofollow">plone.app.stagingbehavior</a> installed. I can check in and check out my custom type, but trying to view the diff results in a stack trace because <a href="https://github.com/plone/plone.app.iterate/blob/master/plone/app/iterate/browser/diff.py" rel="nofollow">plone.app.iterate.browser.diff.DiffView</a> doesn't seem to know how to get the baseline and working copy versions for objects made using dexterity/p.a.stagingbehavior.</p>
  
  <p>I did try overriding DiffView and changing it to use get_baseline and get_working_copy from from <a href="https://github.com/plone/plone.app.stagingbehavior/blob/master/plone/app/stagingbehavior/utils.py" rel="nofollow">plone.app.stagingbehavior.utils</a>, but the diff view still doesn't work (with a different exception, ten thousand levels deep in Products.Archetypes, so I assume it's not likely to work). Perhaps collective.dexteritydiff would help at this point.</p>
  
  <p>It's a bit confusing because p.a.stagingbehavior includes a link to @@iterate_diff in its version of the <a href="https://github.com/plone/plone.app.stagingbehavior/blob/master/plone/app/stagingbehavior/browser/info_baseline.pt" rel="nofollow">plone.app.iterate.checkout_info</a> portlet, which makes me think it's intended to work and maybe my setup is broken or I've done something wrong.</p>