include zone restrictions in item conflict checks

That is, Neopets.com will raise an error when you try to equip a
Kyrii Mage Cape to a pet who's already wearing Ceremonial Shenkuu
Warrior Armour, since the armor restricts the Collar zone which
the cape occupies. DTI, however, would just hide the Collar zone,
as if it were biology. Now, however, DTI will unwear the armor
when you wear the cape, and vice-versa (despite the restriction
relationship being one-directional).