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)


@vighneshbirodkar do you mean we keep the weight 7? =) Which is the min of A-B and A-C.

I think *all* edges should be updated. The function can decide to not do anything if the edges don't conflict. The key is to allow it to make that decision.