fix weighted computations for non-real arrays

[aplavin]

This fixes #518 following suggestion from @nalimilan. The linked issue also contains a long discussion on the best approach, but looks like no decision and fix followed from there. So here I just take the simplest approach to make the computations correct.

[nalimilan]

Thanks. That discussion is indeed quite long. After reading it again, I think that the best solution is to use sum(Base.Broadcast.instantiate(Base.Broadcast.Broadcasted(*, (x, y)))) on Julia 1.4 and above for the generic, non-Real method (see #518 (comment)). The simplest approach is probably to restrict the dot methods you have in this PR to Real (or Number if they are faster for Complex than broadcasting), and use broadcast in the general case.

[andreasnoack]

Superseded by #658