Fixes human/checkarmor getting the armour...

...value for the wrong body part.

Whoever put ran_zone() in there wasn't thinking straight, as it's not
going to affect the part that actually gets damaged.
Armour can turn sharp attacks into blunt ones

Kind of messy, but I couldn't find another way to do it without
reworking a lot of the mob defence procs.
Merge pull request #5293 from mwerezak/armour

Allows armour to turn sharp attacks into blunt attacks with some probability