Add a test for ref(ref(x)).

test/Jamfile.v2

@@ -19,6 +19,7 @@ compile-fail checked_delete_fail2.cpp ;
 
 compile ref_ct_test.cpp ;
 run ref_test.cpp ;
+run ref_ref_test.cpp ;
 compile-fail ref_rv_fail1.cpp ;
 compile-fail ref_rv_fail2.cpp ;
 compile-fail ref_rv_fail3.cpp ;