systemed/iD — pull request #71 by jfirebaugh (2012-11-10 02:58:52+00:00)
Title: Preserve Entity immutability

Reintroduced an Entity class. Entity mutations will be expressed as
methods that return a new Entity.

Extract a move operation from the drag behavior. Instead of updating an
entity in place, the drag event produces a new entity and graph and
replaces the current history version, which was created by doing a noop on
dragstart.

pdata is no longer used. It was previously removed from Graph, and I think
it makes more sense to have a specialized Entity class as well.