AttributeError: 'Patch3DCollection' object has no attribute 'set_sizes'

Hi,

I'm running into a bug with `scatter3D` in mplot3d when ran from python 3.3

I'm using the latest build from github (#e6f899338cb311ad80e89968271944fbdc7b7d7b)

Here is a minimal example:
```python
import numpy as np
import matplotlib.pylab as plt
from mpl_toolkits.mplot3d import Axes3D

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
ax.scatter(np.arange(4), np.arange(4), zs=2)
plt.draw()
```

It fails with the following error:
```python
AttributeError: 'Patch3DCollection' object has no attribute 'set_sizes'

> /home/guillaume/python3/lib/python3.3/site-packages/matplotlib-1.4.x-py3.3-linux-x86_64.egg/matplotlib/collections.py(728)draw()
    727     def draw(self, renderer):
--> 728         self.set_sizes(self._sizes, self.figure.dpi)
    729         Collection.draw(self, renderer)
```
Looks like the `Patch3DCollection` instance doesn't inherits properly from `_CollectionWithSizes`

Best,

Guillaume