tests: Add test for accessing attribute of inherited native type.

tests/basics/subclass-native3.py

@@ -0,0 +1,8 @@
+class MyExc(Exception):
+    pass
+
+e = MyExc(100, "Some error")
+print(e)
+# TODO: Prints native base class name
+#print(repr(e))
+print(e.args)