Conversion of np int64 and float64 to SWIG int and float

Faiss does not transparently convert numpy int64 and float64 / float32 to SWIG's int and float 

```python
import faiss
import numpy as np

a = np.array([4, 6])

d = a[0]
faiss.IndexFlatL2(d) # fails 
faiss.IndexFlatL2(int(d)) # works

```

It should be possible to fix it with SWIG typemaps