Manually abort the underlying TLS connection.

The abort() method calls loseConnection() which tries to shutdown the
TLS connection cleanly. We now call abortConnection() directly which
should promptly close both the TLS connection and the underlying TCP
connection.

I also added some TODO markers to consider cancelling the old previous
timeout rather than checking time.time(). But given how urgently we want
to get this code released I'd rather leave the existing code with the
duplicate timeouts and the time.time() check.