DateParseError on bar plot
`DateParseError` is raised when Series with DateTimeIndex is plotted using bar-plot on axis that already contains another plot:

```
import pandas as pd
df = pd.Series([4,2,1,3,5], index=pd.to_datetime(['2004','2005','2006','2007','2008']))
df.plot()
df.plot(kind='bar')
```

Both of plots work independently, but being called one after another they result in `DateParseError: day is out of range for month`

If called in different order:

```
df.plot(kind='bar')
df.plot()
```

exception is not raised, but x-axis scale is incorrect

pandas version: 0.15.1
numpy verson: 1.9.1
