bpo-31234, socket.create_connection(): Fix ref cycle (#3546)

Lib/socket.py

@@ -711,6 +711,8 @@ def create_connection(address, timeout=_GLOBAL_DEFAULT_TIMEOUT,
             if source_address:
                 sock.bind(source_address)
             sock.connect(sa)
+            # Break explicitly a reference cycle
+            err = None
             return sock
 
         except error as _:

Misc/NEWS.d/next/Library/2017-09-13-18-05-56.bpo-31234.lGkcPg.rst

@@ -0,0 +1,2 @@
+socket.create_connection() now fixes manually a reference cycle: clear the
+variable storing the last exception on success.