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/mkdir.c b/mkdir.c
index 92357a6..eb6e7db 100644
--- a/mkdir.c
+++ b/mkdir.c
@@ -28,6 +28,8 @@
 
 #include <stdio.h>
 #include <errno.h>
+#include <string.h>
+#include <stdlib.h>
 
 static int parentFlag = FALSE;
 static mode_t mode = 0777;