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

coreutils/tail.c

@@ -23,8 +23,12 @@
 
 #include "busybox.h"
 
-#include <sys/types.h>
 #include <fcntl.h>
+#include <getopt.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
 
 static struct suffix_mult tail_suffixes[] = {
 	{ "b", 512 },