UserID is expected to be greater than 199.
If UserID < 400, DoEditPrefs? calls DoNewLogin
Stored in $UserCookie{id}, $UserData{id}
Used by WriteRcLog?, DoPost?, SaveUserData, DoUpdatePrefs?, DoEditPrefs?
Set by LoadUserData, InitCookie, DoNewLogin, DoLogin?
DoOtherRequest action=newlogin sets UserID=0