turn top level constant references into exceptions rather than warnings

gistfile1.diff

diff --git variable.c variable.c
index d142255..27b1237 100644
--- variable.c
+++ variable.c
@@ -1851,7 +1851,7 @@ rb_const_get_0(VALUE klass, ID id, int exclude, int recurse, int visibility)
 		continue;
 	    }
 	    if (exclude && tmp == rb_cObject && klass != rb_cObject) {
-		rb_warn("toplevel constant %"PRIsVALUE" referenced by %"PRIsVALUE"::%"PRIsVALUE"",
+		rb_raise(rb_eNameError, "toplevel constant %"PRIsVALUE" referenced by %"PRIsVALUE"::%"PRIsVALUE"",
 			QUOTE_ID(id), rb_class_name(klass), QUOTE_ID(id));
 	    }
 	    return value;