VIS: plot with `use_index=False` shouldn't plot the index name
Fixes #8558. As far as I can tell the two plot types where this applies are line and bar plots, if there any others they should also be easy to fix. Bar and line plots no longer include the index name:

``` python
import pandas as pd
from pandas import Series
import matplotlib.pyplot as plt

s = Series([1, 2, 3], index=['a', 'b', 'c'])
s.index.name = 'The Index'

ax = s.plot(use_index=False)
plt.show()
```

￼
![image](https://cloud.githubusercontent.com/assets/1460294/5041001/6095c37e-6c0c-11e4-86ca-8e1c4ec83b3c.png)

``` python
ax2 = s.plot(kind='bar', use_index=False)
plt.show()
```

![image](https://cloud.githubusercontent.com/assets/1460294/5041003/657a45d6-6c0c-11e4-92a2-642e5df917a0.png)

@TomAugspurger ?
 Great, thanks @onesandzeroes . FYI there's also AreaPlot but your fix catches it through LinePlot.

Mind rebasing, and I'll merge?
 @TomAugspurger I rebased but got a build error (looks like Travis was having connection issues), not sure how to force a recheck.
 nvm, had to fix up something anyway so it's rebuilding now.
 Thanks. I think there's a button in the Travis GUI to force a rebuild FYI.
