off-center grid in case of stacked bar plot
from [mailing list](https://groups.google.com/forum/#!searchin/pydata/Spacing$20error$20in$20bar$20graphs/pydata/KkIz8evL4As/ft8Puy8UwCwJ)

``` python
df = DataFrame({'A' : [3] * 5, 'B' : range(5)}, index = range(5))
df.plot(kind='bar', stacked='True', grid=True)
```

![example image](http://i.imgur.com/c1AMA.png)
