Add missing include files to avoid implicit function declarations and
resulting compile errors on future compilers.

Submitted upstream: <https://sourceforge.net/p/byghound/bugs/4/>

diff -ur greyhounds-0.8-pre-alpha.orig/src/main.c greyhounds-0.8-pre-alpha/src/main.c
--- greyhounds-0.8-pre-alpha.orig/src/main.c	2022-11-27 17:23:44.579936382 +0100
+++ greyhounds-0.8-pre-alpha/src/main.c	2022-11-27 17:42:59.453179858 +0100
@@ -3,6 +3,7 @@
  * Glade will not overwrite this file.
  */
 
+#include <libintl.h>
 #include "non_gui_defs.h"
 /* reserve storage for global variables */
 dog dogs[420];
@@ -27,6 +28,7 @@
 GtkWidget *main_window;
 #include "interface.h"
 #include "support.h"
+#include "callbacks.h"
 
 int
 main (int argc, char *argv[])