Fix the bug From a bug report.alt.org server, where killing a monster by closing the
castle drawbridge resulted in a panic after the dead monster's possessions
were dropped into the moat and a potion of acid exploded in the process.
water_damage() deleted the object but had no way to tell flooreffects()
that it was gone, so flooreffects() couldn't tell its own caller not to
place and stack the object. After that, a chunk of freed memory became
part of the floor objects chain and eventually triggered a panic which
tried to make a save file but whose reason didn't get logged properly.
a73d997034