Adding numpy count_nonzero & minor template fix

Have i missed something?
Thanks for the clarification. I cannot reproduce your benchmark, but I did another set of benches, using

```python
#pythran export ci(bool[])
import numpy as np
def ci(n):
    return np.count_nonzero(n)
```

and the alternative ``float`` specialization, and here are the results (using your branch)

float:
```sh
>  python -m timeit -s 'import numpy, ci; a = numpy.zeros(1000000)' 'ci.ci(a)'
100 loops, best of 3: 2.55 msec per loop
> pythran ci.py
> python -m timeit -s 'import numpy, ci; a = numpy.zeros(1000000)' 'ci.ci(a)'
1000 loops, best of 3: 845 usec per loop
```

and for the bool version
```sh
> python -m timeit -s 'import numpy, ci; a = numpy.zeros(1000000)' 'ci.ci(a)'
1000 loops, best of 3: 603 usec per loop
> pythran ci.py
> python -m timeit -s 'import numpy, ci; a = numpy.zeros(1000000,dtype=bool)' 'ci.ci(a)'
1000 loops, best of 3: 373 usec per loop
```
so your code is OK. please just remove the useless ``static_cast<...>``, the implict bool conversion in the ``if`` is clearer to me, and does not impact performances.