allow cycles throught the __dict__ slot to be cleared (closes #1469629)

Patch from Armin, test from me.
diff --git a/Misc/NEWS b/Misc/NEWS
index 44683f5..119dfd7 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #1469629: Allow cycles through an object's __dict__ slot to be
+  collected. (For example if ``x.__dict__ is x``).
+
 - Issue #14172: Fix reference leak when marshalling a buffer-like object
   (other than a bytes object).