Compile with libidn support.

--- iputils-s20121125/Makefile.orig	2012-11-26 11:27:31.000000000 +0100
+++ iputils-s20121125/Makefile	2012-11-26 11:28:02.128803095 +0100
@@ -21,7 +21,7 @@
 # sysfs support (with libsysfs - deprecated)
 USE_SYSFS=no
 # IDN support (experimental)
-USE_IDN=no
+USE_IDN=yes
 # Do not use getifaddrs
 WITHOUT_IFADDRS=no
 # arping default device