DF Plots: Error bars don't allow to set styles
With this code the style spec `'o'` is ignored when plotting error bars (#5638):

``` python
In [25]: from numpy.random import randn

In [26]: import pandas as pd

In [27]: df = pd.DataFrame(randn(8,3), columns = "A B yerr".split())

In [28]: df.plot(x='A', y='B',style='o' ,yerr='yerr')
Out[28]: <matplotlib.axes.AxesSubplot at 0x5259cd0>

In [29]: pd.__version__
Out[29]: '0.13.1-791-g07f6d46'
```
