A bit of cleanup, refactoring, and bugfixing...
1) The supernova code now uses enums to represent states, and those state transitions now all happen in `supernova_process` instead of being scattered around.
2) Some state transition bugs were fixed - e.g. the HUD is now disabled when the camera cuts to the external view, instead of when the camera stops moving; and the particles start and the simulation stops when the comments say they do.
3) There is now a game_settings.tbl flag to make the HUD countdown timer reach zero when the supernova hits, instead of reaching 5s. This only affects the HUD display; actual timing is not changed.
4) Don't apply lightshafts if the supernova glare is in effect - partial fix for #4152.
This can be used for producing even leaner builds for standalone
servers. It also provides a nice architecture verification since now
using internal OpenGL functions will cause a compilation or linking
failure.
Taylor Richards