Some player controled animals can now ventcrawl and/or hide

In order to give them a fighting chance in hell of surviving after getting staff of change'd.

The smallest animals get both ventcrawling and hiding, while a few midsized creatures just get ventcrawl. Larger animals (like corgis/cats/cows) get no extra verbs and must rely on their good wits and charm to survive.

handle_ventcrawl has been moved from carbon to living as a side effect of giving some simple animals ventcrawling.