cython fix for #394

I tested this with cython 0.19 and cython 0.20 with a lot of versions of setuptools (below) and it works.

I tried with cython 0.18 and got some compile failures

```
set -e

for v in 0.6c11 0.6c2 0.6c3 0.6c4 0.6c5 0.6c6 0.6c7 0.6c8 0.6c9 0.7.2 0.7.3 0.7.4 0.7.5 0.7.6 0.7.7 0.7.8 0.8 0.9.1 0.9.2 0.9.3 0.9.4 0.9.5 0.9.6 0.9.7 0.9.8 0.9 1.0 1.1.1 1.1.2 1.1.3 1.1.4 1.1.5 1.1.6 1.1.7 1.1 1.2 1.3.1 1.3.2 1.3 1.4.1 1.4.2 1.4 2.0.1 2.0.2 2.0 2.1.1 2.1.2 2.1 2.2 3.0.1 3.0.1 3.0.2 3.0.2 3.0 3.0 3.1 3.1 3.2 3.2 3.3 3.3
do
    git clean -x -f
    pip install setuptools==$v
    python setup.py build
done
```