We add a "dev-restart" command which causes the daemon to close fds
and exec itself. Then we do it after every command, with the caveat
that we always send a commit before newhtlc, because if not committed,
that is forgotten. Fulfillhtlc and failhtlc get resent, since they're
idempotent.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>