Fix tests that were broken from the last commit

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/obj.rs

@@ -905,7 +905,7 @@ fn test_obj_vtable() {
     let to_string_ptr = to_string_ptr.unwrap();
     assert!(obj_is_inst::<MethodInst>(&to_string_ptr));
     with_obj_downcast(to_string_ptr.clone(), |method: &MethodInst| {
-        assert!(method.self_binding.borrow().equals(&*str1.borrow()));
+        assert!(method.self_binding().borrow().equals(&*str1.borrow()));
     });
 
     // now get the method's to_string ptr
@@ -921,7 +921,7 @@ fn test_obj_vtable() {
     assert!(obj_is_inst::<MethodInst>(&method_to_string_ptr));
     with_obj_downcast(method_to_string_ptr.clone(), |method: &MethodInst| {
         assert!(method
-            .self_binding
+            .self_binding()
             .borrow()
             .equals(&*to_string_ptr.borrow()));
     });