contourf hatching and saving to pdf

`contourf` hatches do not appear when saving to pdf. This is apparent in the [`contourf_hatching.py`](http://matplotlib.org/examples/pylab_examples/contourf_hatching.html) example, here:

http://matplotlib.org/mpl_examples/pylab_examples/contourf_hatching_01.pdf

I think something similar was mentioned in #891 and #29, but I'm not sure it was resolved. 
