travis: Test also builds with pypy.
travis: Allow tests with pypy to fail.

Since people usually think of PyPy as a second-class citizen, we don't fail
in case one of our modules barfs with PyPy, but it is certainly a good thing
to test with it (and this author here would love to see PyPy become more
respected as it has the potential to make Python a high performance
language).
travis: Make nose tests verbose.

This way, we can easily see what works by names, instead of only seeing
little dots.