Fix setup26

I'm sorry, I missed again that `include_package_data` is only in `setuptools`.
For some reason the setuptools+cython problem magically disappeared in my python26 installation. Maybe something was fixed in setuptools/python/gcc/cython or somewhere else. Could you check if the problem persists in your setup?
Is it possible to check branches other than master on the CDash board?

If using setuptools is still not possible, I can restore the old `package_data` code.