Use phyradius on planet transit to allow transit on very large planets

It's not currently possible to planetary transit on large worlds since they smash into the planet
I have added phyradius as a distance parameter aswell to avoid smashing.
@salwan feel free to change/patch if you want to.

For testing on large worlds you can add this system to data/systems/custom/ (old elite Archanar with cities)
https://raw.github.com/pioneerspacesim/pioneer/03fd86392b79e3366a907535b939b49de0f81392/data/systems/custom/04_empire.lua

Just change the sector setting to 1,-1,-1 at the bottom so you dont have to travel so far.