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

procps/free.c

@@ -24,6 +24,7 @@
 #include "busybox.h"
 #include <stdio.h>
 #include <errno.h>
+#include <stdlib.h>
 
 extern int free_main(int argc, char **argv)
 {

procps/kill.c

@@ -28,6 +28,7 @@
 #include <unistd.h>
 #include <signal.h>
 #include <ctype.h>
+#include <string.h>
 #include <unistd.h>
 
 static const int KILL = 0;

procps/ps.c

@@ -30,11 +30,13 @@
 
 #include "busybox.h"
 #include <stdio.h>
+#include <stdlib.h>
 #include <unistd.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <ctype.h>
+#include <string.h>
 #include <sys/ioctl.h>
 #define BB_DECLARE_EXTERN
 #define bb_need_help

procps/renice.c

@@ -23,6 +23,7 @@
 #include "busybox.h"
 #include <stdio.h>
 #include <errno.h>
+#include <stdlib.h>
 #include <sys/time.h>
 #include <sys/resource.h>
 

procps/uptime.c

@@ -32,6 +32,7 @@
 #include <stdio.h>
 #include <time.h>
 #include <errno.h>
+#include <stdlib.h>
 
 static const int FSHIFT = 16;              /* nr of bits of precision */
 #define FIXED_1         (1<<FSHIFT)     /* 1.0 as fixed-point */