Investigate why some examples build properly in our gallery despite using numpy and not importing it explicitely.

A recent pull request fixed an import problem in one of our pull request. The example was missing numpy, despite using it. After investigating, the example did generate the plot properly, suggesting some kind of hidden import somewhere.

Here is a link on the build example (Matplotlib 2.0.0)
http://matplotlib.org/examples/mplot3d/pathpatch3d_demo.html