(svn r1421) improved autoreplace multiheaded trains. It now remembers the current heading for an engine instead of turning all of them like the first one and the last the other way

vehicle.c

@@ -1488,6 +1488,8 @@ int32 CmdReplaceVehicle(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 
 		/* We do not really buy a new vehicle, we upgrade the old one */
 		if (v->engine_type != new_engine_type) {
+			byte old_engine = v->engine_type;
+			byte sprite = v->spritenum;
 			byte cargo_type = v->cargo_type;
 			v->engine_type = new_engine_type;
 			v->max_age = e->lifelength * 366;
@@ -1498,13 +1500,13 @@ int32 CmdReplaceVehicle(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 			// using if (true) to declare the const
 				{
 				const RailVehicleInfo *rvi = RailVehInfo(new_engine_type);
+				const RailVehicleInfo *rvi2 = RailVehInfo(old_engine);
 				byte capacity = rvi->capacity;
 
-				if (rvi->flags & RVI_MULTIHEAD && v->next == NULL ) {
-					v->spritenum = rvi->image_index + 1;	// +1 is the mirrored end of the dualheaded engines
-				} else {
-					v->spritenum = rvi->image_index;
-				}
+				/* rvi->image_index is the new sprite for the engine. Adding +1 makes the engine head the other way
+				if it is a multiheaded engine (rear engine)
+				(sprite - rvi2->image_index) is 1 if the engine is heading the other way, otherwise 0*/
+				v->spritenum = rvi->image_index + (sprite - rvi2->image_index);
 				
 				v->cargo_type = rvi->cargo_type;
 				v->cargo_cap = rvi->capacity;