!2098 (merged) made exitlevel a cheat no matter what in co-op, which doesn't make a lot of sense considering #1104 (closed). This merge request fixes that by making exitlevel only considered a cheat under certain circumstances.
Those circumstances are:
While in single player, consistent with the map command.
While in a special stage, as you gain nothing from exiting a special stage early. It's basically the same as failing one.
During the credits, since apparently you can use the command during them for some reason.
If at least one player in multiplayer has already beaten the level, which is consistent with setting playersforexit to one.
If the level being exited to is a level that has not been unlocked yet, consistent with the map command.
Unfortunately, this does not solve #1104 (closed) entirely as record attack emblems are still cheese-able by exiting a level you've already beaten in multiplayer. I personally see this as outside the scope of this merge request, and will be handling it separately.
