When s6-rc stops a service, it also stops everything that
depends on it. but when it starts a service it starts only
that service, so we have to go through the other services
depending on it and figure out if they should be started too.
- uncontrolled services that are not dependent on a controlled service
- controllers
- _not_ controlled services or any other service that depends on one
Instead of treating the trigger as the "main" service and the
triggered service as subsidary, now we treat the triggered
service as the service and the trigger as "subsidary". This
needs some special handling when we work out which services
go in the default bundle, but it works better for declaring
dependencies on triggered services because it means the
dependency runs after the triggered service comes up, not
just when the watcher-for-events starts