Rolling boulder traps and pacifism

If you stepped on an unknown rolling boulder trap, and that rolling boulder
hit a monster and killed it, you would be called a killer.  This makes
playing a pacifism conduct game rather difficult.
- track boulders from unknown rolling boulder traps, and don't charge/credit
hero if they kill monsters. This is done by temporarily setting otrapped on
such boulders.
- boulders from known traps are still charged/credited to the hero
- fix a couple places in ohitmon where is_poisonable wasn't checked along
with opoisoned.

doc/fixes34.1

@@ -29,6 +29,7 @@ let lev_comp and dgn_comp accept optional carriage return character prior to
 Wizard of Yendor will start harassing you after the invocation if you've
 	managed to get that far without ever killing him
 characters polymorphed into centaurs can't wear boots
+if an unknown rolling boulder trap kills a monster, you shouldn't be a murderer
 
 
 Platform- and/or Interface-Specific Fixes