Fix some issues noticed when experimenting with ceiling hiders.
They're all blind (at least without the monks' Eyes) and some of
the behavior while blind seemed to be incorrect (though some that
I thought was wrong turned out to be ok; feel_newsym() won't update
the map if the hero can't reach the floor). Fixing that made me
notice that some terrain side-effects (being underwater or stuck in
lava) weren't getting disabled when the underlying terrain wasn't
the corresponding type anymore.
projects / nethack / commit