The initial intention was to rely on stable sorting when several events have
the same key. For this to happen, sorting must not continue the comparison with
the second item of events.

This could lead to data corruption (conflict resolution with wrong base):

  FAIL: testNotifyReplicated (neo.tests.threaded.test.Test)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "neo/tests/threaded/__init__.py", line 1093, in wrapper
      return wrapped(self, cluster, *args, **kw)
    File "neo/tests/threaded/test.py", line 2019, in testNotifyReplicated
      self.assertEqual([15, 11, 13, 16], [r[x].value for x in 'abcd'])
    File "neo/tests/__init__.py", line 187, in assertEqual
      return super(NeoTestBase, self).assertEqual(first, second, msg=msg)
  failureException: Lists differ: [15, 11, 13, 16] != [19, 11, 13, 16]

  First differing element 0:
  15
  19

  - [15, 11, 13, 16]
  ?   ^

  + [19, 11, 13, 16]
  ?   ^