fixes the problem with reference assignment.
honestly stolen from a post on the cython forum:

A simple (and ugly) workaround for reference assignment:

```
     cdef void test(int& out):
         (&out)[0] = 123
```

[see pose](https://groups.google.com/forum/#!searchin/cython-users/assign$20reference/cython-users/j58Sp3QMrD4/c-rlLByjCCgJ)
(cherry picked from commit ca34f43)