We have some duplication in handling queues, so this is an attempt at
deduplicating some of that work. `daemon_conn` now uses the
`msg_queue` and `channeld` was also migrated to `msg_queue`. At the
same time I made `msg_queue` create a copy of the messages or takes
over messages marked with `take()`. This should make cleaning up
messages easier.
This uses a single fd for both status and control.
To make this work, we enforce the convention that replies are the same
as requests + 100, and that their name ends in "_REPLY".
This also means that various daemons can simply exit when done; there's
no race between reading request and closing status fds.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>