Region Adjacency Graph

## Example Images
![figure_1](https://cloud.githubusercontent.com/assets/3823490/3291718/5ce9b952-f587-11e3-8c29-e2aace6d7794.png)
![figure_2](https://cloud.githubusercontent.com/assets/3823490/3291723/7074b134-f587-11e3-8c73-d28222891a21.png)


First, write "Cannot", not "Can't" and certainly not "Cant". =)

Second, why not? =) I had this restriction once in my own RAG class but then I figured out it was unnecessary, and merging non-adjacent nodes can be useful e.g. in cases of occlusion, or where the initial segmentation has made an error that we can correct.