Fails to start: UndoManager has no python implementation

[Mark Howard]

I've just installed gaphor on a up to date dapper machine. It fails to start:

$ gaphor

** (gaphor:23872): WARNING **: couldn't make the type `CanvasGroup' ready
/usr/lib/python2.4/site-packages/diacanvas/__init__.py:13: RuntimeWarning: tp_compare didn't return -1 or -2 for exception
  from _canvas import *
TypeError: Cannot create a consistent method resolution
order (MRO) for bases GObject, CanvasGroupableIface, CanvasGroupable
/usr/lib/python2.4/site-packages/diacanvas/__init__.py:19: DeprecationWarning: Module gnome.canvas is deprecated; please import gnomecanvas instead
  from view import *
/usr/lib/python2.4/site-packages/gaphor/undomanager.py:195: RuntimeWarning: Interface type UndoManager has no python implementation support
  gobject.type_register(UndoManager)
Traceback (most recent call last):
  File "/usr/bin/gaphor", line 10, in ?
    gaphor.main(model)
  File "/usr/lib/python2.4/site-packages/gaphor/__init__.py", line 48, in main
    import diagram
  File "/usr/lib/python2.4/site-packages/gaphor/diagram/__init__.py", line 56, in ?
    from classifier import ClassifierItem
  File "/usr/lib/python2.4/site-packages/gaphor/diagram/classifier.py", line 18, in ?
    from nameditem import NamedItem
  File "/usr/lib/python2.4/site-packages/gaphor/diagram/nameditem.py", line 9, in ?
    from elementitem import ElementItem
  File "/usr/lib/python2.4/site-packages/gaphor/diagram/elementitem.py", line 74, in ?
    initialize_item(ElementItem)
  File "/usr/lib/python2.4/site-packages/gaphor/diagram/__init__.py", line 39, in initialize_item
    if (diacanvas.CanvasItem in bases) or \
AttributeError: 'module' object has no attribute 'CanvasGroup'