environs/config: Remove PreferIPv6() method and "prefer-ipv6" setting
environs/config: Remove PreferIPv6() method and "prefer-ipv6" setting

anastasiamac/juju,reedobrien/juju,waigani/juju,mikemccracken/juju,waigani/juju,axw/juju,waigani/juju,dooferlad/juju,dimitern/juju,reedobrien/juju,bz2/juju,howbazaar/juju,ericsnowcurrently/juju,marcmolla/juju,bz2/juju,howbazaar/juju,kat-co/juju,alesstimec/juju,mikemccracken/juju,mjs/juju,macgreagoir/juju,macgreagoir/juju,marcmolla/juju,bac/juju,AdamIsrael/juju,perrito666/juju,frankban/juju,marcmolla/juju,mjs/juju,marcmolla/juju,dooferlad/juju,gabriel-samfira/juju,reedobrien/juju,dimitern/juju,kat-co/juju,bac/juju,macgreagoir/juju,mikemccracken/juju,alesstimec/juju,dooferlad/juju,gabriel-samfira/juju,alesstimec/juju,frankban/juju,axw/juju,mjs/juju,kat-co/juju,ericsnowcurrently/juju,gabriel-samfira/juju,bz2/juju,mikemccracken/juju,bz2/juju,ericsnowcurrently/juju,perrito666/juju,mjs/juju,reedobrien/juju,mikemccracken/juju,bac/juju,anastasiamac/juju,ericsnowcurrently/juju,dooferlad/juju,gabriel-samfira/juju,anastasiamac/juju,frankban/juju,howbazaar/juju,dimitern/juju,anastasiamac/juju,howbazaar/juju,reedobrien/juju,macgreagoir/juju,dooferlad/juju,bac/juju,gabriel-samfira/juju,perrito666/juju,howbazaar/juju,marcmolla/juju,bac/juju,mjs/juju,macgreagoir/juju,axw/juju,kat-co/juju,frankban/juju,bz2/juju,waigani/juju,anastasiamac/juju,kat-co/juju,axw/juju,AdamIsrael/juju,AdamIsrael/juju,frankban/juju,dimitern/juju,alesstimec/juju,perrito666/juju,perrito666/juju,AdamIsrael/juju,ericsnowcurrently/juju,mjs/juju,alesstimec/juju,mjs/juju,axw/juju,dimitern/juju