Comment 8 for bug 1501217

I've some half-formed ideas:

- if apt allows a shell command instead of just an executable name, maybe the config could be

    Acquire::http::ProxyAutoDetect "if [ -x /usr/share/squid-deb-proxy-client/apt-avahi-discover ]; then /usr/share/squid-deb-proxy-client/apt-avahi-discover; fi";

- if apt doesn't use the shell, but allows a command with arguments, and not just an executable name, maybe the config could be

    Acquire::http::ProxyAutoDetect "sh -c 'if [ -x /usr/share/squid-deb-proxy-client/apt-avahi-discover ]; then /usr/share/squid-deb-proxy-client/apt-avahi-discover; fi'";

- if apt is truly restricted to just a single executable name in that parameter, maybe the package could ship a small wrapper script that conditionally runs /apt-avahi-discover if it exists, with the wrapper script placed somewhre in /etc, so it's not removed on purge, e.g.

    Acquire::http::ProxyAutoDetect "/etc/squid-deb-proxy-client/apt-avahi-discover";

with /etc/squid-deb-proxy-client/apt-avahi-discover containing

    # you're not expected to modify this, see LP: #1501217
    if [ -x /usr/share/squid-deb-proxy-client/apt-avahi-discover ]; then
        /usr/share/squid-deb-proxy-client/apt-avahi-discover
    fi

I keep not finding the time to experiment and see if one of the first two ideas would work. I don't like the 3rd option.