Bug#827928: [pkg-go] Bug#827928: Bug#827928: golang-github-coreos-go-systemd-dev: circular dependency with golang-github-coreos-pkg-dev

[Michael Hudson-Doyle]

Thanks to upstream changes we can fix this by packaging
golang-github-coreos-pkg-capnslog separately from the rest of
golang-github-coreos-pkg. It's a bit of a hack, it'd be better to wait
until upstream splits out capnslog into a separate repo but that seems
to be taking a while. I'll do this in Ubuntu first an propose it for
fixing in Debian if it works out :-)