A better solution to the "jumping" corpses bug

As it turns out, my previous fix broke speed calculations, so entities were moving at weird angles. In this PR, I've reverted my old solution and wrote a new one. Corpses (and now loot) are aligned to a grid with units the size of 1/(2^4) for nice floating point operations. That should cover 99% of stationary objects that would be subject to the jumping bug.

I think we'll also want to use this function whenever an entity or hazard becomes stationary to cover that remaining 1%. But I haven't found a suitable place to do that yet.