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
diff --git a/kill.c b/kill.c
index 19ca187..3eb829a 100644
--- a/kill.c
+++ b/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;