Comment 1 for bug 479705

With some help from Robert, I've written a patch to do this. Because merge lines already have an optional revspec field, and it's hard to distinguish subdir names from revspecs, the optional subpath comes after the revspec. i.e. to merge a debian dir of tip, you need a line like:

merge packaging lp:ubuntu/foo/debian -1 debian

It's a bit hackish. Suggestions for improvements are welcome.