There is a comment above the function indicating that it should be
aligned with hero ammo breakage, but this wasn't the case. One big
difference is that any monster-thrown or -shot object would be deleted
unconditionally if it hit another monster trapped in a pit. I don't
know why that was in there, but it's not present in hero ammo breakage
chances, and it meant that a monster could sling the Mines luckstone at
the hero, hit a monster in the pit, and permanently lock the hero out of
getting the luckstone (as just happened to a player during the current
tournament). This pulls the hero breakage rules out into their own
function and uses that for monster breakage as well, to make sure they
are aligned. I also refactored drop_throw a bit to reduce the number of
separate variables tracking whether the object was deleted (was create,
objgone, and retvalu), and changed its (and ohitmon's) type to boolean.
d42564bacd