The three cases we care about only happen on specific transitions:
1. They can no longer spend our failed HTLC: we can fail the source now.
2. They are fully committed to their new HTLC htlc: we can forward now.
3. They can no longer timeout their fulfilled HTLC: the funds are ours.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
All the daemons will use a common seed for point derivation, so drag
it out of lightningd/opening.
This also provide a nice struct wrapper to reduce argument count.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This object is basically the embodyment of BOLT #2. Each HTLC already
knows its own state; this moves them between states and keeps them
consistent.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
