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

wc.c

@@ -23,6 +23,7 @@
 #include "busybox.h"
 #include <stdio.h>
 #include <getopt.h>
+#include <stdlib.h>
 
 static int total_lines, total_words, total_chars, max_length;
 static int print_lines, print_words, print_chars, print_length;