This is less convenient to use, but makes far more sense for a real
user (like a wallet). It can ask about the route, then decide whether
to use it or not.
This will make even more sense once we add a parameter to control how
long we let the HTLC be delayed for, so a client can query for high,
medium and low tolerances and compare results.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
