Re-run res_init() when resolv.conf changes

libc caches the contents of resolv.conf, so if it changes (eg, because
the network state changed), we need re-run res_init().

http://bugzilla.gnome.org/show_bug.cgi?id=584246

gio/gnetworkingprivate.h

@@ -56,6 +56,10 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 
+#ifndef _PATH_RESCONF
+#define _PATH_RESCONF "/etc/resolv.conf"
+#endif
+
 #endif
 
 G_BEGIN_DECLS