Check newly created consistency using _PyUnicode_CheckConsistency(str, 1)

 * In debug mode, fill the string data with invalid characters
 * Simplify also reference counting in PyCodec_BackslashReplaceErrors()
   and PyCodec_XMLCharRefReplaceError()
diff --git a/Python/compile.c b/Python/compile.c
index 79d1d21..10e9ad2 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -263,6 +263,7 @@
         Py_DECREF(result);
         return NULL;
     }
+    assert(_PyUnicode_CheckConsistency(result, 1));
     return result;
 }