monster ranged attacks (trunk only)

monster ranged attacks (trunk only)

     Newsgroup posts mention "boulder forts" from time to time, where the
player surrounds the hero with boulders in order to prevent the majority
of monsters from being able to attack.  Since the hero can shoot or throw
or zap over/around/through boulders, monsters ought to be able to do so
too.  This makes the test for whether a monster is lined up properly for
its ranged attacks try harder when the original line-of-sight check fails.
If there aren't any terrain obstacles found, it allows a chance to attack
based on the number of locations in the path that contain any boulders.
Giants and any monster carrying a boulder-destroying wand of striking get
to ignore boulders, overriding the random chance.