horizontal histogramm doesn't work in 1.2 branch

```python
x = np.random.rand(100)
plt.hist(x, orientation='horizontal')
plt.show()
```
gives the following error on the 1.2 branch

 plt.hist(x, orientation='horizontal')
  File "/space/python_packages/lib/python2.7/site-packages/matplotlib/pyplot.py", line 2672, in hist
    stacked=stacked, **kwargs)
  File "/space/python_packages/lib/python2.7/site-packages/matplotlib/axes.py", line 8180, in hist
    color=c, bottom=bottom)
TypeError: barh() got multiple values for keyword argument 'bottom'