Use R_PointToDist2 instead

Apparently overflows less often

Actually, lets just fix FixedHypot instead.

Now FixedHypot uses the code from R_PointToDist2, and R_PointToDist2 just calls FixedHypot.

Ultimately, this branch was intended to get rid of a redundant way to retrieve distance and replace it with the one that was actually good at its job. So consolidating FixedHypot and R_PointToDist2 together is just an extension of that.