In case of cross posting on mailing-lists handled by patchwork we have
duplicated msgids in the DB. So we need to make a choice when asked for
the patch with a give msgid. Otherwise:

Internal Server Error: /patch/msgid/1461691808-12414-20-git-send-email-daniel.vetter@ffwll.ch/
Traceback (most recent call last):
  File "django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "patchwork/views/patch.py", line 128, in msgid
    patch = get_object_or_404(Patch, msgid='<' + msgid + '>')
  File "shortcuts.py", line 155, in get_object_or_404
    return queryset.get(*args, **kwargs)
  File "django/db/models/query.py", line 338, in get
    (self.model._meta.object_name, num)
MultipleObjectsReturned: get() returned more than one Patch -- it returned 2!

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>