Fix header file usage -- there were many unnecessary header files included in
busybox.h which slowed compiles.  I left only what was needed and then fixed up
all the apps to include their own header files.  I also fixed naming for pwd.h
and grp.h functions.  Tested to compile and run with libc5, glibc, and uClibc.
 -Erik
diff --git a/sleep.c b/sleep.c
index 10eca59..61b7ce4 100644
--- a/sleep.c
+++ b/sleep.c
@@ -23,6 +23,8 @@
 
 #include "busybox.h"
 #include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
 
 extern int sleep_main(int argc, char **argv)
 {