(svn r3535) -Feature: [autoreplace] allow autoreplacing of train wagons

currently ALL available wagons are displayed in the right menu in the replace window
	however the replacement will only be done if the new wagon can be refitted to carry same cargo as the old one is currently carrying

	Since the standard vehicles do not have any valid wagon replacements, this feature can only be used when using newgrf sets

window.h

@@ -353,6 +353,7 @@ typedef struct {
 	byte sel_index[2];
 	EngineID sel_engine[2];
 	uint16 count[2];
+	bool wagon_btnstate;	// true means engine is selected
 } replaceveh_d;
 assert_compile(WINDOW_CUSTOM_SIZE >= sizeof(replaceveh_d));