Include sys/wait.h to avoid warnings.

Index: login.c
--- login.c.orig
+++ login.c
@@ -6,7 +6,7 @@
 
 
 #include "ytree.h"
-/* #include <sys/wait.h> */  /* maybe wait.h is available */
+#include <sys/wait.h>  /* maybe wait.h is available */
 
 
 
