The way we build transactions, serialize them, and compute fees depends on the
chain we are working on, so let's add some context to the transactions.
Signed-off-by: Christian Decker <decker.christian@gmail.com>
These utilities allow us to create valid test txs and information given both
sides' complete set of secrets.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>