This patch is actually a WIP. I'd ideally like it if it could also
detect the addition of `(git-file-name ...)` and add that to the
sub-header commit message portion, but I am not so talented in Yasnippet
creation :).

If anybody wants to take a crack at it, please do. But I think this
snippet will prove useful as we will almost always have unstable
tarballs coming into our sources.