non-uniform weights should be working again

This fixes a bug which was introduced in v1.1.0.

When we first began using numpy to speed up the matrix operations (introduced in v1.1.0), we forgot to incorporate weights in one part of the code. So the python code worked when uniform weights were used (which occurs by default). But we forgot to make sure that non-uniform weights are working.

This code has finally been fixed, and the testing code has been updated.