audit small applets and mark some of them as NOFORK.

Put big scary warnings in relevant places.

coreutils/usleep.c

@@ -9,11 +9,10 @@
 
 /* BB_AUDIT SUSv3 N/A -- Apparently a busybox extension. */
 
-#include <stdlib.h>
-#include <limits.h>
-#include <unistd.h>
 #include "busybox.h"
 
+/* This is a NOFORK applet. Be very careful! */
+
 int usleep_main(int argc, char **argv);
 int usleep_main(int argc, char **argv)
 {