Report that go is not installed on non dpkg-based distros.

This allows building Go packages on distros that aren't Debian
derivatives (e.g. Arch), for later distribution to Ubuntu servers.
gofmt.
Merge pull request #1 from danderson/master

Let `godeb download` work on non-dpkg distros.
Merge branch 'master' into v1.
golang.org/dl/ changed the storage location again.