(svn r6393) -Fix: [autoreplace] now refit costs are added to the estimated costs (could spend more than allowed when estimate and actual cost were not the same)

-Fix: [autoreplace] fixed a very rare failure when building an engine could cost more than the player could pay before selling the old one
   this happened when the replacing the front cost so much that the the rear end didn't have enough money to build as expected
   now the estimate keeps track of the price for the wagons/engines in front of the unit it's currently looking at
-Codechange: [autoreplace] added function to learn if and what cargo type to refit to. Needed to allow the estimation to tell refit costs

openttd.h

@@ -279,6 +279,7 @@ enum {
 
 	NUM_CARGO       = 12,
 
+	CT_NO_REFIT     = 0xFE,
 	CT_INVALID      = 0xFF
 };