- no more recursively traversing portals, as this can overflow the stack
- better outside filling and .pts file generation, inspired by q3map
(do a bfs from all leafs with entities, storing the number of steps
from an occupied leaf in each leaf. Then do a dfs from the outside node
to the first entity we hit.)
- .por file writing was dropped for now, can be re-added later
240d65f788