Linus Torvalds [off-list ref] writes:
I _think_ you should be able to just do
git pull <repodir> <branchname>
where <repodir> can even be just "." for the very same repository.
I've not tested it, but dammit, it should work. If it doesn't, it's a bug.
I know it works. 'git pull . somebranch' is the command I use
the second most often in the git suite (the first being
git-show-branch).