commands.resolve: call driverpreprocess if we haven't run it yet We need to be careful about allowing --mark and --unmark to keep working -- we don't want the user to be stuck in a weird state. The exact behavior here is still to be decided, though.

merge.applyupdates: call driverconclude after performing merge actions This will be a chance for the merge driver to finish resolving or generating any driver-resolved files. As before, having a separate error state from 'unresolved' is too big a refactoring for now, so we hack around it by setting unresolved to a positive value when necessary.