message: Update wamp_session.cc
  By updating the session ID prior to state change, we see less of the "session #0" logging messages.  Also updated logging/exceptions to generally lower case convention.
diff: @@ -668,8 +668,8 @@ void wamp_session::process_message(json_array& ja,
  }
  else if (message_type == msg_type::wamp_msg_welcome)
  {
  - change_state(state::sent_auth, state::sent_hello, state::open);
  handle_WELCOME(ja);
  + change_state(state::sent_auth, state::sent_hello, state::open);
  if (is_open())
  notify_session_open();
  return;
  @@ -1143,7 +1143,7 @@ void wamp_session::handle_WELCOME(json_array& ja)
  check_size_at_least(ja.size(), 3);
  if (!ja[1].is_uint())
  - throw protocol_error("Session ID must be unsigned integer");
  + throw protocol_error("router provided session ID must be unsigned integer");
  const t_session_id sid = ja[1].as_uint();
  if (sid == WAMP_SESSION_ID_UNSET)
  @@ -1151,7 +1151,7 @@ void wamp_session::handle_WELCOME(json_array& ja)
  m_sid = sid;
  m_log_prefix = generate_log_prefix(m_sid);
  - LOG_INFO(m_log_prefix << "Router assigned session ID: '" << m_sid << "'");
  + LOG_INFO(m_log_prefix << "session ID assigned by router WELCOME");
  /* TODO router announces its supported Roles and Features in the 'extra'
  * dictionary: this would be the place to extract it... */
  