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/dutmp.c

@@ -21,6 +21,8 @@
 #define bb_need_io_error
 #include "messages.c"
 #include <utmp.h>
+#include <stdlib.h>
+#include <unistd.h>
 
 extern int dutmp_main(int argc, char **argv)
 {
@@ -35,7 +37,7 @@ extern int dutmp_main(int argc, char **argv)
 	} else  {
 		file = open(argv[1], O_RDONLY);
 		if (file < 0) {
-			error_msg_and_die(io_error, argv[1], strerror(errno));
+			perror_msg_and_die(io_error, argv[1]);
 		}
 	}
 

miscutils/mktemp.c

@@ -25,6 +25,8 @@
 #include "busybox.h"
 #include <stdio.h>
 #include <errno.h>
+#include <unistd.h>
+#include <stdlib.h>
 
 extern int mktemp_main(int argc, char **argv)
 {

miscutils/mt.c

@@ -1,6 +1,7 @@
 /* vi: set sw=4 ts=4: */
 #include "busybox.h"
 #include <stdio.h>
+#include <stdlib.h>
 #include <sys/mtio.h>
 #include <sys/fcntl.h>
 

miscutils/readlink.c

@@ -25,6 +25,7 @@
 #include "busybox.h"
 #include <errno.h>
 #include <unistd.h>
+#include <stdlib.h>
 
 int readlink_main(int argc, char **argv)
 {

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__ */
 

miscutils/watchdog.c

@@ -23,6 +23,8 @@
 #include "busybox.h"
 #include <stdio.h>
 #include <fcntl.h>
+#include <unistd.h>
+#include <stdlib.h>
 
 extern int watchdog_main(int argc, char **argv)
 {