relnotes: add 6.7rc0

relnotes: remove outdated message from `next`

branching: merge default into stable for 6.7rc0

branching: merge stable into default

perf: add a --as-push option to perf::unbundle This turned out to make a quite significant difference.

chainsaw-update: exit early if one of the intermediate command fails That will prevent the user to be presented with a start that pretend to be consistent with the request, but is not.

chainsaw-update: lock the repository for the duration of the operation This should prevent and catch some misusage where something else try to touch the repository.

chainsaw-update: taking care of initial cloning Perhaps we should go just a bit lower level than this `instance()`, since the main added value in our use-case is full path resolution, that we need to do anyway for the rmtree cleanup.

chainsaw-update: use a graph with branching in graph This will be relevant for the next improvement of `chainsaw-update`.

chainsaw-update: log actual locks breaking Previously, the command would simply state that it was about to break locks, not if there was actually some to break. This version is race-free. It would be also possible to display the content of the lock before hand (not race-free but informative in almost all cases).