Nothing showed what waited for a build machine, and an ask could not be
dropped without leaving the plan that made it waiting for ever. New verbs:
queue, cancel, clear, rebuild, replay, kill, pause, resume, and plans retry.
Every ask a person drops is recorded failed through the same take-in as a
failed build; a plan keeps the id it asked each module under and matches
its outcome by it. replay is a dry run unless registered, and registering
an older commit than one registered since needs --older (hq issue 207).
A plan waiting on a seat paused on every holder says so and is not late;
a failed plan can be retried, and a rebuild joins the plan holding the
module instead of running beside it.
jochen
106507b1d3