At startup, we load the outpoints to watch, *then* roll back 15
blocks. If there were things in those blocks we wanted to watch, we
no longer do!
1. We load the utxoset into memory: everything in the utxoset table
which has spendheight null.
2. We roll back 15 blocks to re-read. Deleting a block from the
database causes the utxo spentheights referring to it to be set
to null.
3. We roll forward, but we didn't update the in-memory utxoset,
so we're not watching those utxos which are spent.
The main symptom of this is that we spam peers with obsolete gossip
(if we get sent a channel announcement for a closed channel, we can
think it isn't spent yet). But it could *also* mean we don't notice
onchain txs, if we restart at the wrong time!
Changelog-Fixed: lightningd: we could miss tx spends which happened in the past blocks when we restarted.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
1e66414b9e