merge.applyupdates: create absentfilectxes for change/delete conflicts At the moment no change/delete conflicts get to this point -- we're going to make that happen in an upcoming patch.

mergestate: add methods to queue files to remove, add or get These are meant for use by custom merge drivers that might want to modify the dirstate. Dirstate internal consistency rules require that all removes happen before any adds -- this means that custom merge drivers shouldn't be modifying the dirstate directly.

resolve: record dirstate actions after performing resolutions Some resolutions might lead to pending actions we need to perform in the dirstate -- so perform them.

mergestate: add a way to record pending dirstate actions We're going to use this in resolve in the next patch.

merge.recordupdates: don't require action keys to be present in dict We're going to use this function for a much smaller set of actions in the next patch. It's easier to do this than to backfill the dict we pass in.

histedit: constant-ify the constraints list Used a class as a namespace, and then wired up a classmethod to return all known constraints. I'm mostly happy with this, even though it's kind of weird for hg.

histedit: add an experimental base action This is a first (very simple) version of the histedit base action. It works well in common usecases like rebasing the whole stack and spliting the stack. I don't see any obvious edge cases - but probably there is more than one. That's why I want to keep it behind experimental.histeditng config knob for now. I think on knob for all new histedit behaviors is better because we will test all of them together and testers will need to turn it on only once to get all new nice things.

histedit: add abortdirty function Small helper function for aborting histedit when left with dirty working directory.

histedit: add forceother constraint For the future 'base' action in histedit we need a verification constraint which will not allow using this action with changes that are currently edited.

histedit: make verification configurable Before we can add a 'base' action to histedit need to change verification so that action can specify which steps of verification should run for it. Also it's everything we need for the exec and stop actions implementation. I thought about baking verification into each histedit action (so each of them is responsible for verifying its constraints) but it felt wrong because: - every action would need to know its context (eg. the list of all other actions) - a lot of duplicated work will be added - each action will iterate through all others - the steps of the verification would need to be extracted and named anyway in order to be reused The verifyrules function grows too big now. I plan to refator it in one of the next series.