Add setting for transfer payment mode from source, minus transfers.

This is to reduce large negative payments for the final leg.

src/settings_type.h

@@ -529,6 +529,7 @@ struct EconomySettings {
 	bool   smooth_economy;                   ///< smooth economy
 	bool   allow_shares;                     ///< allow the buying/selling of shares
 	uint8  feeder_payment_share;             ///< percentage of leg payment to virtually pay in feeder systems
+	bool   feeder_payment_src_station;       ///< calculate leg payment relative to the source station, not the leg source
 	byte   dist_local_authority;             ///< distance for town local authority, default 20
 	bool   exclusive_rights;                 ///< allow buying exclusive rights
 	bool   fund_buildings;                   ///< allow funding new buildings