lightningd can crash on shutdown if it's in the middle of getchaintips;
we free the conn, the finished callback is called (process_chaintips),
and it reports that it received an empty result.
The simplest fix is to set a flag in the struct bitcoind destructor,
and avoid the callback.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Also, we split the more sophisticated json_add helpers to avoid pulling in
everything into lightning-cli, and unify the routines to print struct
short_channel_id (it's ':', not '/' too).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
