bpo-36820: Break unnecessary cycle in socket.py, codeop.py and dyld.py (GH-13135)

Break cycle generated when saving an exception in socket.py, codeop.py and dyld.py as they keep alive not only the exception but user objects through the ``__traceback__`` attribute.


https://bugs.python.org/issue36820



Automerge-Triggered-By: @pablogsal

Lib/socket.py

@@ -839,7 +839,11 @@ def create_connection(address, timeout=_GLOBAL_DEFAULT_TIMEOUT,
                 sock.close()
 
     if err is not None:
-        raise err
+        try:
+            raise err
+        finally:
+            # Break explicitly a reference cycle
+            err = None
     else:
         raise error("getaddrinfo returns an empty list")