Update the `bitcoin_tx_add_input` interface to accept a witness script
and or scriptPubkey.
We save the amount + witness script + witness program (if known) to
the PSBT object for a transaction when creating an input.
1. Use status_debug() instead of status_unusual() for when we can't make a
penalty tx (this happens easily the time if we fund a channel).
2. Use status_failed() (which exits) instead of status_broken() (which doesn't!)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>