Fixup stairs in Chokoban
Put !ambrosia on DD autopickup (Arrhythmia)

Since it's very very good for them. (Possibly too good...!?)
Add Shadow Creature traps

Summon a few creatures from the current level whenever the player
or a monster in LOS steps on the trap, roughly as a casting of
Shadow Creatures. The monsters are always hostile to the player.

The number of monsters spawned increases with depth.
Don't draw shock serpent discharges on solid features.

It was causing odd visual glitches.
Fix compilation.

GGGRRRUUUNNNTTT
Properly initialise shock serpent discharge effect tile.

More correctly, tell the beam code to init it for us.
Improve elemental evoker inert text
Display xp evoker discharged sprites again
Remove an obsolete function