Fix increased refcount in test__socket_dns.py for PY3
Fix increased refcount in test__timeout.py for PY3
Fix increased refcount in test__greenlet.py for PY3
Fix increased refcount in test__api_timeout.py for PY3
Fix increased refcount in test__exc_info.py for PY3
Fix increased refcount in select.py for PY3
Fix increased refcount in backdoor.py for PY3
Fix increased refcount in test__subprocess.py for PY3
Fix increased refcount in event.py for PY3
Fix increased refcount in test__core.py for PY3