fix implicit declaration compilation warning

Index: src/htmltcl.c
--- src/htmltcl.c.orig
+++ src/htmltcl.c
@@ -42,6 +42,7 @@ static char const rcsid[] = "@(#) $Id: htmltcl.c,v 1.2
 #include "html.h"
 #include "restrack.h"
 #include "swproc.h"
+#include "restrack.h"
 
 #include <time.h>
 
