This tests against a bug that was triggered when a linked to object got
removed without also removing the reference to it somehow.  See
http://dev.plone.org/plone/ticket/8349 and http://dev.plone.org/plone/ticket/8390
for additional information.

As usual, we need to create the necessary links first:

  >>> self.setRoles(('Manager',))
  >>> self.setText(portal.doc1, '<a href="doc2">a document</a>')

Next we remove the linked-to object, but without removing the according
reference to it.  To do that we need to suppress the normally fired events.
Normally this should never happen, but as the tickets report there are some
ways to get end up with dangling reference like this:

  >>> portal._delObject('doc2', suppress_events=True)

Now the reference should be broken:

  >>> portal.doc1.getReferences()
  [None]

If we now try to update the linking document again in order to remove the
link, things used to break raising a ``ReferenceException``.  This should
be handled more gracefully now:

  >>> self.setText(portal.doc1, 'foo!')
  >>> portal.doc1.getReferences()
  []