We create a temporary tx which is a child of the real tx, for simplicity of
marshalling. That's OK.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
In particular, the main daemon needs to pass it about (marshal/unmarshal)
but it won't need to actually use it after the next patch.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>