changeset_printer: use changectx to get status tuple log.parents() can't handle wdir() revision. Because repo.status() creates ctx objects, there would be no benefit to get parent node from changelog.

changeset_printer: replace _meaningful_parentrevs() by changeset_templater's Because changeset_printer needs pctx object anyway, there would be no benefit to avoid creation of pctx in _meaningful_parentrevs().