* The Space Cube is now generated at world start, before away missions are loaded
This means away missions don't have space transitions
* The setup_map_transition proc is protected from excessive tiles proceeding (the proc is set to the background if too much tiles are processed)
* Added a comment explaining the Space Cube, by Incoming
* Fixes #4903 : "mobs don't maintain momentum on z-level transition"
* Serendipitiously fixes #2614
Merge pull request #5082 from Menshin/space_transitions_fixes

Space transitions/Away missions loading fixes