This effectively turns off avahi-browse by default; doing it by
default is not worth it compared to the number of various (mostly
slowness) problems it has caused people, for example Alioth #312691
and RedHat #630326.
Mandriva has applied a similar patch for some time already, although
their environment variable name was different ($COMP_AVAHI_BROWSE).
`_known_hosts_real' will add hosts from HOSTFILE (compgen -A hostname), unless
`COMP_KNOWN_HOSTS_WITH_HOSTFILE' is set to an empty value.
To run the unit tests:
$ cd test && ./runUnit _known_hosts_real.exp
