misc/dist: add 'label' part of distro name, include blog content

This will allow us to cut binaries with names like:
        go1.2rc1.darwin-amd64-osx10.6.pkg
        go1.2rc1.darwin-amd64-osx10.8.pkg

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/13629045