3d plot examples

Hello again,

in mplot3d.py I changed line 729:

- if Z:
+if Z==None:

Could this work too??? 'Python mplot3d.py' seems to work then but 'python
surface.py' fails with:

jens-ifw@...913...:/media/exchange/Python/3d> python surface.py
Traceback (most recent call last):
  File "surface.py", line 16, in ?
    ax = mplot3d.Axes3D(fig, axisbg='k')
AttributeError: 'module' object has no attribute 'Axes3D'

Cheers

Jens