Ipns dag restructuring

[whyrusleeping]

Im creating this issue as a place to discuss how the datastructures associated with ipns should interact and behave when modified.

[whyrusleeping]

Currently, when i modify a file, it modifies the existing DAG object. The problem is that if another object has a pointer to the node i modified, it might access data that is not what it is expecting, One solution is to rewrite the entire tree (keeping unchanged nodes) on a write. This modifies every parent node of the modified node up to the root.

[whyrusleeping]

The other decision is whether or not we want to do this change immediately, or buffer them and do them all when the publish timeout triggers.