Force SSLv3 on smtplib.starttls() on Python 3.4

I was getting this error on Python 3.4:

```python
Traceback (most recent call last):
  File "/usr/lib/python3.4/site-packages/rss2email/email.py", line 161, in smtp_send
    smtp.starttls()
  File "/usr/lib/python3.4/smtplib.py", line 688, in starttls
    server_hostname=server_hostname)
  File "/usr/lib/python3.4/ssl.py", line 364, in wrap_socket
    _context=self)
  File "/usr/lib/python3.4/ssl.py", line 578, in __init__
    self.do_handshake()
  File "/usr/lib/python3.4/ssl.py", line 805, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: TLSV1_ALERT_DECODE_ERROR] tlsv1 alert decode error (_ssl.c:598)
```