Add an option to /tool fetch to save output to a variable

dhcpv6 client doesn't appear to work with pppoe-client interfaces, which is how my ISP (Internode) provides IPv6 addresses, and I'm not even sure if you guys support IPv6 on the PPPoE client yet. http://ipv6.internode.on.net/access/adsl/ Having support for this would be epic. same here in NZ, was h...