'rot' parameter to DataFrame.boxplot not applied to some axes when multi-panel plot is produced using 'by'
Minimal snippet:

``` python
import pandas as pd
from numpy.random import randn
import matplotlib.pyplot as plt

d = pd.DataFrame({'one':randn(5), 'two':randn(5), 'three':randn(5), 'label':['label'] * 5},
        columns = ['one','two','three', 'label'])
bp= d.boxplot(by='label', rot=45)
plt.savefig('xxx.png')
```

Output produced:
![xxx](https://f.cloud.github.com/assets/128034/1884064/fcb7cd40-7993-11e3-8a07-58d7613407e2.png)

Issue:
The label on the left is rotated but the label on the right is not.

Versions: 
pandas '0.12.0'
matplotlib '1.3.1'
