histedit: modify rollup to discard date from the rollup commit (issue4820) This change adjusts and documents the new behaviour of 'roll'. It now fits nicely with the behaviour of 'commit --amend' and the 'edit' action, by discarding the date as well as the commit message of the second commit. Previously it used the later date, like 'fold', but this often wasn't desirable, for example, in the common use case of using 'roll' to add forgotten changes to a changeset (because 'hg add' was previously forgotten or not all changes were identified while using 'hg record').