ENH: Intuitive Barplot Series Ordering
Modifies the horizontal bar plot behavior to plot series in order from top-to-bottom.

Plotting a regular bar graph from a DataFrame object will plot each series of data from left-to-right in the same order as presented in the legend from top-to-bottom. When plotting a horizontal bar graph the series of data are plotted from bottom-to-top, which is the reverse of the legend and unintuitive. 

Pandas allows a `legend='reverse'` option which reverses the order of the legend and preserves series colors, but does not fix the unintuitive bottom-to-top ordering of series.
###### Pandas Standard `barh` Behavior:

![original_behaviour](https://cloud.githubusercontent.com/assets/3064019/7130265/1a2724a0-e23b-11e4-8940-9f54d8cd14c2.png)
###### Desired `barh` Behavior:

![alternate_behaviour](https://cloud.githubusercontent.com/assets/3064019/7130270/324a4242-e23b-11e4-9b29-f4bcb60c3b14.png)
###### Pandas Standard `barh` `legend='reverse'` Behavior:

![reversed_legend](https://cloud.githubusercontent.com/assets/3064019/7130274/4b5d2ec0-e23b-11e4-88e4-48e938c8e7a8.png)

Thanks for the informative summary (with pictures). I think the current behavior comes from us drawing from the origin outward. This makes sense when going left to right, not so much bottom to top.

I'd rather we have another keyword argument for this, since it will be an API change, something like `bar_order` or `group_order`.

It will be a bit before I can review the code.
 I think the behavior can be generalized if plot can accept `sort_columns='reverse'` (like legend does). It may useful for other stacking and pie charts.
 pls rebase/update. closing, but reopen if you want to work on.
