Monsters with rust attacks (rust monster) and corrosion attacks
(black pudding, gray ooze) can eat or otherwise destroy iron bars
but xorns could only move through the iron bars spot without being
able to eat the metal there. Change xorn to eat bars instead of
phazing through them. Lets rock moles eat bars too.
Hero polymorphed into a rust monster would eat bars if trying to
move to their location but couldn't do so if already there (maybe
was in xorn form and now in rust monster form). Xorns could pass
through them but not eat them. Allow hero metallivores to eat
bars at the current location via 'e', similar to eating food off
the floor. Hero as rock mole behaves like rust monster.
0e713dc4e9