(svn r8978) -Feature: Rewrite of transfer system.

This major feature-fix keeps track of the value of transfers offloaded at a station, and hands on to a loading vehicle a credit note proportionate to the cargo loaded. The transferring vehicle is paid only for the distance it has travelled. eg. B-C in a transfer chain A-B-C-D.
When the final cargo is delivered, these credit notes are cashed, and the final vehicle is paid for A-D minus any credit notes it is carrying. The company bank balance increases by the value of the A-D route.
You still need to set up a profitable route; it is still easy to make a loss on transfers by bad planning. :)

src/vehicle.h

@@ -298,6 +298,8 @@ struct Vehicle {
 
 	int32 profit_this_year;
 	int32 profit_last_year;
+	int32 cargo_feeder_share;      ///< value of feeder pickup to be paid for on delivery of cargo
+	TileIndex cargo_loaded_at_xy;  ///< tile index where feeder cargo was loaded
 	uint32 value;
 
 	union {