next: add a --evolve option When on a topological head, this option will trigger the evolution of a unstable changeset that will result in a children of the current working copy parent. This should ease stacked changesets workflow by allowing to stick to prev and next to move through a stack of diff, evolving part of it on demand when needed. In case of ambiguity, the command will ask the user to choose. We need a better definition of "the stack of changesets I'm working on" to be able to seamlessly handling branching.