Improves rand_zone() and miss chance procs
Fixes apply_effect() used without armour checks
Fixes human armor value for full body effects not being weighted by body part

This was an issue because it meant that not having hand or feet
protection reduced the player's protection from full body effects much
more than it should have, and meant that not having your hands protected
was just as bad as not having your chest protected.
Fix for rad suits not protecting against radiation

Rad suits were not providing complete protection from radiation. This is
probably not the best solution. Better solutions would be to either add
the HANDS and FEET coverage flags as done here in addition to updating
the sprite to reflect the additional coverage, or to add radiation proof
gloves and boots as part of the radiation suit set (potentially
problematic for taj and unathi engineers).