BUG: spatial.distance: always convert to float in sqeuclidean
BUG: spatial.distance: always convert to float in sqeuclidean

Integers are subject to silent wraparound in the subtraction and
squaring operations, as pointed out by @jakevdp. Some unnecessary
copying may occur, but any call where both arguments are float
arrays still only allocates a single temporary array.

datamade/hcluster,datamade/hcluster,datamade/hcluster