Couldn't this just be `find_all_dirs | sed 's,^\.,github.com/dotcloud/docker,g'` ?

To play golf a little further, I think this whole function could even be shortened completely to `find_all_dirs | sed 's,^\.,github.com/dotcloud/docker,g' | paste -d, -s`.  There's probably some way to make sed do more work, but this is the simple solution that jumps out at me.