merge: consider successor changesets for a bare update Previously, a bare update would ignore any successor changesets thus potentially leaving you on an obsolete head. This happens commonly when there is an old bookmark that hasn't been moved forward which is the motivating reason for this patch series. Now, we will check for successor changesets if two conditions hold: 1) we are doing a bare update 2) *and* we are currently on an obsolete head. If we are in this situation, then we calculate the branchtip of the successor set and update to that changeset. Tests coverage has been added.

merge: refactor initialization of variables in update There is no code change here but this helps prepare for future commits that will fix a bare update with obsolete markers.

merge: update comment for future devs

obsolete: clarify documentation for succcessorssets