next: prompt user to choose child in ambiguity in `hg next --evolve` This patch makes `hg next --evolve` prompt user to choose a child to evolve and update when multiple of them exists. This is improvement over previous behavior where we used to error out saying ambiguous next unstable changeset and told user to manually use `hg evolve -r rev`. While writing this patch, I am personally very happy to have this feature as I have encountered this stage many times and I wanted `next --evolve` to take care of that. It uses the revselectionprompt thing added in earlier patches.

next: move logic to evolve the children to it's own function This patch moves the logic which evolves the children and updates to it in `hg next --evolve` to it's own function as we want to use that again.

next: prompt user to choose a children in case of ambiguity This patch adds functionality to prompt user and ask the children to which next should move to incase of multiple childrens. This is a very nice UI because otherwise user has to lookup changeset hash, and then manually do `hg update` to that. In this case we show hash and description so user can choose which one to update easily. It is using the interactive revision choosing functionality added in a previous patch.

next: show changeset hash in `--dry-run` instead of rev numbers Rev numbers can change, hence we should show rev hash instead of rev numbers in dry-run.