added a missing header file

git-svn-id: svn://bind10.isc.org/svn/bind10/trunk@976 e5f2f494-b856-4b98-b285-d166d9295462

src/lib/dns/cpp/rdata.h

@@ -21,6 +21,8 @@
 
 #include <boost/shared_ptr.hpp>
 
+#include <exceptions/exceptions.h>
+
 namespace isc {
 namespace dns {
 class InputBuffer;