rtfc 0.7.1

Fixed

• A message sent the instant a session opened could fail with closed_before_ack when the
  receiver was slow to read the hello: the receiving side lost the first bytes of the frame
  behind it and dropped the session. The hello now goes through the session's own reader,
  so nothing behind it is lost.
• A problem recording the addresses a contact sends in its hello no longer closes the
  session; the message still arrives, and the problem is logged.