(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/train_gui.cpp

@@ -503,6 +503,8 @@ static void DrawTrainDetailsWindow(Window *w)
 				DrawString(x, y + 2, FreightWagonMult(i) > 1 ? STR_TOTAL_CAPACITY_MULT : STR_013F_TOTAL_CAPACITY, 0);
 			}
 		}
+		SetDParam(0, v->cargo_feeder_share);
+		DrawString(x, y + 15, STR_FEEDER_CARGO_VALUE, 0);
 	}
 }