Up until now, riskfactor was useless due to implementation bugs, and
also the default setting is wrong (too low to have an effect on
reasonable payment scenarios).
Let's simplify the definition (by assuming that P(failure) of a node
is 1), to make it a simple percentage. I examined the current network
fees to see what would work, and under this definition, a default of
10 seems reasonable (equivalent to 1000 under the old definition).
It is *this* change which finally fixes our test case! The riskfactor
is now 40msat (1500000 * 14 * 10 / 5259600 = 39.9), comparable with
worst-case fuzz is 50msat (1001 * 0.05 = 50).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Several users have noticed that they cannot pay satoshis.place or similar places
that have tiny payment amounts if they are not directly connected. This is due
to the forwarding fee dominating the transferred amount.
This commit adds a new option, exempting tiny fees (up to 5 satoshis by default)
from having to pass the maxfeepercent flag. While we could have told users to
tweak maxfeepercent I think it is usefull to have a default exemption.
[Squashed --RR]
These error codes will cause `pay` to retry, so `pay` will never
actually report those error codes.
Those error codes will only get reported at the `sendpay` level.
