(svn r2290) - CodeChange: protect the next batch of commands. This brings us to a total of 61, which is 53% :)

- CodeChange: To correctly accept engine-prototypes, the best-player checking has been moved to its own function, I hope it functions the same as before.
- CodeChange: Added symbolic types of PlayerID, OrderID and EngineID. For engines also added GetEngine() and IsEngineIndex(), similar to the other such functions.
- CodeChange: To correctly build industries, some tables have been moved to build_industry.h. The only way to find out currently if an industry is valid in a climate is by looping all industries and checking if it matches. Also to comply with the patch setting build_rawmaterial_industries, it is assumed that these industries do not accept any cargo of any type. This can and probably should changed in the future to some flag in their struct. Also use _opt_ptr instead of _opt.
- CodeChange: implemented the HQ checking code inspired by MarkR2 in "[ 1190944 ] Many commands not checked for security".  Unfortunately it is impossible to prevent only deleting a HQ by a modified client atm.
- CodeChange: For insert order and modify order their parameters are implicitely truncated to 8 bits, instead of the 16 bits said in the comments.

train_cmd.c

@@ -1478,8 +1478,10 @@ int32 CmdTrainGotoDepot(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 	return 0;
 }
 
-/* p1 = vehicle
- * p2 = new service int
+/** Change the service interval for trains.
+ * @param x,y unused
+ * @param p1 vehicle ID that is being service-interval-changed
+ * @param p2 new service interval (0 - 65536)
  */
 int32 CmdChangeTrainServiceInt(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 {
@@ -1489,8 +1491,7 @@ int32 CmdChangeTrainServiceInt(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 
 	v = GetVehicle(p1);
 
-	if (v->type != VEH_Train || !CheckOwnership(v->owner))
-		return CMD_ERROR;
+	if (v->type != VEH_Train || !CheckOwnership(v->owner)) return CMD_ERROR;
 
 	if (flags & DC_EXEC) {
 		v->service_interval = (uint16)p2;