Formatting dates & timestamps
The following:

``` python
import pandas.io.data as web
df =  web.DataReader(["AAPL", "MSFT", "EBAY", "AMZN", "CSCO", "GOOG", "YHOO", "AOL", "IBM"], "yahoo", start='2014-10-1').to_frame()['Close']
df.index = df.index.droplevel('minor')
df = df.reset_index()

# > df.head()
#        Date   Close
#0 2014-10-01   99.18
#1 2014-10-01  317.46
#2 2014-10-01   43.47
#3 2014-10-01   25.03
#4 2014-10-01   55.46

f, ax = plt.subplots(figsize=(10,4))
df.boxplot(by='Date', ax=ax)
ax.xaxis.set_major_locator(matplotlib.dates.WeekdayLocator(byweekday=(0,1,2,3,4,5,6),interval=7))
ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter('%b\n%d'))
```

results in:
![screen shot 2014-11-03 at 11 52 14 am](https://cloud.githubusercontent.com/assets/1993919/4886140/c8550dbc-6379-11e4-911b-3a6139bd504c.png)

As you can see, the `set_major_locator` and `set_major_formatter` commands failed. This is with 0.15 and the latest `Python 3.4.1 :: Anaconda 2.1.0 (x86_64)`. 

Is this a bug? How can I specify a  **tick frequency** and **formatting** for timestamps for boxplots **created by Pandas**? Does Pandas have any equivalent commands? Is there any way to massage the indices so that I can still apply `set_major_locator` and `set_major_formatter`?
