abort with reused session

[dajt1725]

My code creates a session and makes a number of requests by using session.post() After ~50 successful requests I get an abort in the requests_negotiate code ("assert isinstance(sock, (ssl.SSLSocket, socket.socket))") because sock is None, which isn't an instance of ssl.SSLSocket. As a workaround I keep a counter, and create a new session every 49 requests, but that's inelegant.