Fix for Issue #80: Integer Division with Arrays

This fixes #80. Numpy has an issue with the /= operator for integers:

```python
>>> a = np.array([1])

>>> b = np.array([2])

>>> a/b  # Correct
array([ 0.5])

>>> a/=b

>>> a  # Different from a/b
array([0])
```

This is a workaround. I will post this issue to the numpy repository.