- change the compiled-in defaults and adjust the default's configfile
        commented-out example settings to match compiled-in defaults, instead
        of changing the defaults only in the configfile, as per #179432
    - fix #179574 by providing a default uidl_format for pop3
    - half-fix #179620 by having plaintext auth enabled by default... this
        needs more thinking (which one we really want) and documentation either
        way