WIP: matplotlib: 1.2.1 -> 1.3.0

FIXME: ipython --pylab=qt stops working (ImportError: No module named
matplotlib). Also, I had to change --prefix=$out to --root=$out just to
make it build (tip from Archlinux forum).

What's new in 1.3.0:
http://matplotlib.org/users/whats_new.html#new-in-matplotlib-1-3

API changes in 1.3.x:
http://matplotlib.org/api/api_changes.html#changes-in-1-3