straddling in and out of the void.
Previously, we were just deleting these faces, leaving HOMs.
Keeping them but filling the leaf in as solid doesn't work either, because
if they are the only faces left in the leaf it messes up the content type
determination later.
Fixes test_tjunc01.map test case from Qmaster.
- 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
Eric Wasylishen