Avoid traceback reference cycle in TALInterpreter.do_onError_tal

In Python 3, exceptions have a ``__traceback__`` attribute containing
their associated traceback.  Storing an exception in a local variable of
a frame present in that traceback thus creates a reference cycle.  Avoid
this by explicitly deleting the exception value when we're finished with
it.

1 files changed, 1 insertions, 1 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index db87896..89411df 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,7 +5,7 @@
 4.5 (unreleased)
 ================
 
-- Nothing changed yet.
+- Avoid traceback reference cycle in ``TALInterpreter.do_onError_tal``.
 
 
 4.4 (2018-10-05)