evolve: add a `--stop` flag for `hg evolve` command This patch adds a `--stop` flag for `hg evolve` command. The stop flag lets you stop the evolution from where you are and let you move to other things if you want. This fuctionality is great as user can decide to resolve conflicts later on, stop the command execution, do something else and get back once they has time or care about resolving them. As implementation details, it clears the evolvestate, updates to the parent of working directory clearing the uncommitted changes which also deletes the mergestate. A new test file test-evolve-stop.t is added with tests of the new flag added.