[BUG?] Paths not being tracked properly

When we try to add a Node to a parent Node a second time, we expect an error like this, as in

``` js
var logo = scene.addChild();
scene.addChild(logo);
```

, we expect an error like this:

```
Uncaught Error: Node is already mounted at: body/0
```

However, I've got some complex code that is removing and adding child nodes often, and at some point, when I use `Node#addChild` to add a Node to a parent Node, I'm getting this error from PathStore instead:

```
Uncaught Error: item already exists at path: [data-reactid=".0"][data-scene-id="1"]/0/97/0/0/0/0/0/1
```

The "item" in question happens to be a Transform who's path is being (re)added `TransformSystem#registerTransformAtPath`, based on the stack trace:

```
ncaught Error: item already exists at path: [data-reactid=".0"][data-scene-id="1"]/0/97/0/0/0/0/0/1
at PathStore.insert (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:2117:16)
at TransformSystem.registerTransformAtPath (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:240:21)
at Node.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:3503:26)
at Dispatch.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:1644:64)
at Node.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:3512:15)
at Dispatch.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:1644:64)
at Node.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:3512:15)
at Dispatch.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:1644:64)
at Node.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:3512:15)
at Dispatch.mount (http://localhost:3000/client/lib/_famous/famous.entry.js?bab126b262ed37f8bcf79944013b074b89476f49:1644:64)
```

This leads me to believe that the path system might have a bug because I'm strictly using only `Node#addChild`/`Node#removeChild`. At some points between those calls I'm adding and removing Position and Rotation components.