Ticket 49171 - Nunc Stans incorrectly reports a timeout
    
    Bug Description:  In some cases nunc-stans would incorrectly report
    and IO timeout.
    
    Fix Description:  Make the io output type volatile to prevent re-arranging
    of the code. We then make timeout exclusive to read, write and signal.
    Finally, we add an extra check into ns_handle_pr_read_ready that
    asserts we truly have an idle timeout. It issues a warning now
    instead if this scenario occurs, rather than closing the
    connection.
    
    https://pagure.io/389-ds-base/issue/49171
    
    Author: wibrown
    
    Review by: mreynolds (thanks!)