Use feels_like_helping() in dosupport(), lnd_support()
feels_like_helping() case cn == foe is missing in the code it
replaces. No difference in behavior, because:
* cn == foe && cn == friend can't happen. Because you can't get into
ground combat against yourself (assault, attack and paradrop don't
let you), friend != foe for support.
* cn == foe && cn != friend behaves the same: no support.
feels_like_helping() returns 0 because of the explicit case. The
replaced code doesn't support because cn can't be at war with
itself.