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

backout: add a message after backout that need manual commit In some case Backout silently succeeded to back out but left all the change uncommitted. This may be confusing for user so this changeset add a note reminding to commit. Other backout case already actively informs the user about created commit.