[wip][CR] Zombie slave (Zlave)

Feature for `CANNIBAL` and `PSYCHOPATH` traits.

>If you don't like this idea, then you are a normal person, not cannibal or psychopath.

What is idea? If you watch episodes Walking Dead, thou me will understand.

![zlaves](https://cloud.githubusercontent.com/assets/6351438/3561395/6c5e239a-09bf-11e4-9098-a3144b972416.png)

Zlave is a zombie with cutted hands and teeth. He can not grab you, bash you and bite you.

So, I think, only cannibals and psychopaths can do same with corpses.

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Gameplay:

* Begin playing with  `CANNIBAL` or `PSYCHOPATH` traits.
* Search for `zombie brute`. Why only zombie brute. Its discutable, well brute's are strong and fast and has many pheromone (read next about it). To be honest, the whole thing in balance. 
* Kill `zombie brute`
* Use your knife on corpse. If you `CANNIBAL` or `PSYCHOPATH`, then in knife menu appear new entry:
![knife](https://cloud.githubusercontent.com/assets/6351438/3561431/74cb8e36-09c0-11e4-8eae-c297d9f9f22f.png)

* Done. On the ground appears new corpse with cut hands and teeth. Wait until it revives.

After reviving zlave will follow you, but not attack.

Interact with zlave:
![menu](https://cloud.githubusercontent.com/assets/6351438/3561433/dd0fac48-09c0-11e4-8ab4-a5be37ec93fc.png)

* You can try to swap positions with zlave (chance depend on `str`+`dex`)

* You can tear out pheromone ball from zlave. It killed zlave, but near zombies can be friendly.

* You can attach to zlave one bag and push to it some items (used the multidrop interface). The capacity of the bag is taken.

* You can drop *all* items to ground. You can't look into bag robed on zlave, you can only drop the bag on ground with all stuff.

* upd: new feature (not on screenshot): you can tie/untie zlave if you have short rope.

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Well, this feature increased coolness of cannibals and psychopaths, and roleplaying of DDA - more features of surviving in the post-apocalyptic zombie world.

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Me and my new three f(r)iends goes to liquor store:

![friends](https://cloud.githubusercontent.com/assets/6351438/3561471/84e9a908-09c3-11e4-9837-5b816b911ad0.png)

kevingranade
>I haven't checked, but I'm pretty sure if you get too far away from your zlaves, they'll get unloaded, which will clear their effects and destroy their inventories.

Let zlaves has no abilities to go on stairways.