Partially accomodate multi-floor staircases
Permit more than one stair in each direction
Pick the correct arrival stairs when switching levels
Generate dungeons with correctly connected stairs

With randomly many stairs and some of them up and down stairs at once,
this is not trivial.
Don't split the random seed when generating levels

Levels are no longer kept lazy (they are sent to clients early),
so we can simplify this.
Replace Descend k by Ascend (-k)
Number levels below ground with negative integers
Fix killing clients from old games
Avoid single up-and-down stairs on a level
Prevent AI from almost always choosing ascending over descending
When destroying an actor, wipe out his target
Prevent repeated triggering of features, e.g, stairs
Make AI switch leaders less often

and for better reasons.
Keep leader after using stairs and switch away from stuck leaders
Let AI spawners have active arenas

-- Even spawners and horrors need an active arena
-- for their leader, or they start clogging stairs.
Lower human IQ until pathfinding is implemented
Make AI more likely to step on stairs
Fix wrong time of client levels
Tweak AI leader switches