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 89b6471..bbf224b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -9,6 +9,9 @@
 Core and Builtins
 -----------------
 
+- Issue #1469629: Allow cycles through an object's __dict__ slot to be
+  collected. (For example if ``x.__dict__ is x``).
+
 - Issue #13521: dict.setdefault() now does only one lookup for the given key,
   making it "atomic" for many purposes.  Patch by Filip GruszczyƄski.