`rotation` parameter has no effect on `RegularPolyCollection`

It looks like the `rotation` parameter in `RegularPolyCollection` was disconnected in the following commit: https://github.com/matplotlib/matplotlib/commit/b8726d09026ba7507d8501de0fbd921ec2d1243e

Below is an example that *should* display squares with different rotations, but doesn't on master or 1.4.0.

```python
import matplotlib.pyplot as plt
from matplotlib.collections import RegularPolyCollection
import numpy as np


xx, yy = np.mgrid[:10, :10]
xy_points = np.transpose([xx.flatten(), yy.flatten()])
rotations = np.linspace(0, 2*np.pi, len(xy_points))

fig, ax = plt.subplots()
for xy, alpha in zip(xy_points, rotations):
    col = RegularPolyCollection(4, sizes=(100,), rotation=alpha,
                                offsets=xy, transOffset=ax.transData)
    ax.add_collection(col, autolim=True)
ax.autoscale_view()

plt.show()
```