May a bug of `Series.plot` in pandas 0.17?
The origin post with pictures is on: http://stackoverflow.com/questions/33559772/is-this-a-bug-of-series-plot-in-pandas-0-17

I always use `ser.plot(xticks=range(0, len(ser), step), ..)` to plot figures with specified xticks. But it doesn't work anymore in pandas 0.17 when the Series with labels. Here are the codes:

``` python
In [1]: from numpy import random as rnd 
In [2]: import pandas as pd
In [3]: pd.__version__
Out[3]: '0.17.0'
In [4]: %matplotlib inline
In [5]: rnd.seed(123)
In [6]: ser = pd.Series(rnd.randn(73).cumsum(), index=['P%02d' % i for i in range(73)])
In [7]: ser.plot(figsize=(9, 6), rot=60, title='Figure without xticks')
Out[7]: <matplotlib.axes._subplots.AxesSubplot at 0x8370198
In [8]: ser.plot(figsize=(9, 6), xticks=list(range(0, 73, 6)), rot=60, title='Figure with xticks')
Out[8]: <matplotlib.axes._subplots.AxesSubplot at 0x83e9940>
```

![image](https://cloud.githubusercontent.com/assets/511719/10991679/4acedd1c-849a-11e5-89d0-f6264b788849.png)
![image](https://cloud.githubusercontent.com/assets/511719/10991682/4d695a16-849a-11e5-9db3-6ff885a22234.png)

The figure with xticks specified doesn't display xticklabes correctly.
