<Someone> wrote:
> "You kill the invisible storm giant. The boulder fills a pit."
> [...] why did I find the corpse *lying on* and not *buried in* the
> former pit?
Ensure that the corpse ends up buried in that case.
Added a random factor to arrow, dart and rock traps so they'll eventually
stop producing new objects. Also fixed a bug in mklev that set the trap
"once" flag even for traps where it wasn't currently appropriate.