For performance, we delay entering the 'wallet_payment' into the db
until we actually commit to the HTLC (when we have to touch the DB
anyway).
This opens a race where we can try to pay twice, and since it's not in
the database yet, we don't notice the duplicate.
So remove the temporary payment field from htlc_out, which was always
an uncomfortable hack, and make the wallet code abstract over the
deferred entry a little by maintaining a 'unstored_payments' list
and incorporating that in results.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
38e8601cf6