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

modutils/rmmod.c

@@ -25,6 +25,9 @@
 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <linux/unistd.h>
 #define __LIBRARY__