Isolate unit tests under their own make directive.
As a side-effect of using amount_msat in gossipd/routing.c, we explicitly handle overflows and don't need to pre-prune ridiculous-fee channels. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>