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

miscutils/update.c

@@ -32,11 +32,14 @@
 #include <sys/param.h>
 #include <sys/syslog.h>
 #include <unistd.h> /* for getopt() */
+#include <stdlib.h>
 
 
 #if defined(__GLIBC__)
 #include <sys/kdaemon.h>
 #else
+#include <sys/syscall.h>
+#include <linux/unistd.h>
 static _syscall2(int, bdflush, int, func, int, data);
 #endif /* __GLIBC__ */