put /usr/local/sbin back in $PATH so `brew doctor` is happy

note: put the paths in /etc/paths too, for launchd, gui apps
add some more homebrew commands to beew completion

home-brew ships with some external commands that previously
needed to be installed manually. nice.

see https://github.com/Homebrew/homebrew/wiki/External-Commands
/etc/paths so launched and gui apps get $PATH set too