Adds check for threshold status and calls off the turret

for clearly non-human characters.

Incentive to not take Alpha, too, since those still pass for human.  BMG turrets are designed for vehicles so can target HUGE folks.  Tank turret is handled in the multi_robot scripting.

And now gives LOUD WARNINGS so you can turn around (or play Fastest Finger if you're up for that).
I'd like the turret to at least start defending itself if attacked.  It's ridiculously OP otherwise.