This tests the programmatically removal of a referred to item or rather its
prevention because of link integrity. First we need to create the link in
question:

  >>> self.setRoles(('Manager',))
  >>> doc = portal.doc1
  >>> img = portal.image1
  >>> self.setText(doc, img.tag())
  >>> self.assertEqual(doc.getReferences(), [img])

Then we try to delete the image using ObjectManager's `manage_delObjects`,
which should raise an exception:

  >>> portal.manage_delObjects(ids=['image1'])
  Traceback (most recent call last):
  ...
  LinkIntegrityNotificationException: <img src="http://nohost/plone/image1/image" ... />

Since the implementation is based on `IObjectRemovedEvent` on the real objects
now (as opposed to on the special references used before), the above exception
is raised only after the item in question ('image1') was already deleted from
the folder, and on top of that the exception was expected, the testrunner will
consider the test successful and therefore not abort the current transaction.
This results in the image being deleted, even though an exception was raised
during the call.  Hence we cannot change the document and try removing the
image again as we did in earlier versions of this test. In real life (i.e.
outside the testrunner) the exception would cause the transaction to be
aborted, of course.

