Issue 3611: in some cases (a __del__ re-raising an exception, when called from inside
an 'except' clause), the exception __context__ would be reset to None.
This crases the interpreter if this precisely happens inside PyErr_SetObject.

- now the __context__ is properly preserved
- in any case, PyErr_SetObject now saves the current exc_value in a local variable, to
avoid such crashes in the future.

Reviewer: Antoine Pitrou.
diff --git a/Misc/NEWS b/Misc/NEWS
index 3927f9b..5372f0b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #3611: An exception __context__ could be cleared in a complex pattern
+  involving a __del__ method re-raising an exception.
+
 - Issue #2534: speed up isinstance() and issubclass() by 50-70%, so as to 
   match Python 2.5 speed despite the __instancecheck__ / __subclasscheck__
   mechanism. In the process, fix a bug where isinstance() and issubclass(),