RF: make .travis.yml use travis Python and wheels

We were using erlang as language and apt-get for dependencies, because
of the difficulty getting numpy, scipy onto the travis slaves when using
the standard travis Python virtualenvs.

Now travis has numpy in the virtualenvs, and astropy, nipy.bic have
wheels for the travis slaves, so installation is much quicker.  This
commit switches back to using the travis Python testing machinery.
BF: fix graph setup.py to refer to Cython file

It was assuming the C file was built, but should instead refer to the
pyx file and let numpy.distutils do the rest.
BF: update c files from Cython sources

Tests failing on Python 3 because of old Cython builds.