VIS: plot with `use_index=False` shouldn't plot the index name
```
n [1]: df = pd.Series([1, 2, 3], index=['a', 'b', 'c'])

In [2]: df.index.name = 'The Index'

In [5]: df.plot(use_index=False)
Out[5]: <matplotlib.axes._subplots.AxesSubplot at 0x10b1a1438>
```

![gh](https://cloud.githubusercontent.com/assets/1312546/4639393/2e6af314-540c-11e4-9d07-6c5ab8250aae.png)

The x axis label
