Issue #19543: Added Py3k warning for decoding unicode.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 9368a3a..2925651 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1288,6 +1288,9 @@
         goto onError;
     }
 
+    if (PyErr_WarnPy3k("decoding Unicode is not supported in 3.x", 1) < 0)
+        goto onError;
+
     if (encoding == NULL)
         encoding = PyUnicode_GetDefaultEncoding();