Introduce new node status (NODE_LOGOUT), which is used for the status of a node
after a user (has been) disconnected and before the node transitions to waiting for connection (WFC) status. Usually the duration of this status is very short, but it can be longer (e.g. for running log-out module and event) and for (new) msg-scan pointer fix-ups. Updated logout() to remove some cruft and add some more log/debug output. Automatic new-scan pointer fix-ups when performing new-message scans (if the current pointer is greater than the last message number, set it to the last message number) and when saving message pointers. Passing user_t* to get/putmsgptrs() instead of message number now (to better detect Guest account).