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.
../../tests/test-tutorial.t