Set equal aspect ratio in 3D plots

I need to produce 3D plots with equal aspect ratio for all axes. I have tried to a kluge to achieve this approximately in **vegan** package where I use these functions, but the exact aspect ratio cannot be guaranteed. However, it seems that `scatterplot3d` could be "easily" patched to achieve this goal. 

I had made this work on version 0.33-3, and the current set of patches was first applied on that version in githug (6cff54b), and then the later development was merged onto these patches. It all seems to go smoothly.