Codechange: Let the compile generate the master command table out of templated command traits.

This is using a non-intrusive type-traits like templated system, which
allows compile-time validation that the command table and the command
enum match up.

src/object_cmd.cpp

@@ -33,6 +33,7 @@
 #include "newgrf_debug.h"
 #include "vehicle_func.h"
 #include "station_func.h"
+#include "object_cmd.h"
 
 #include "table/strings.h"
 #include "table/object_land.h"