Neither http nor rsync transports know about the 'alternates'
mechanism yet, so if a downloader does:
$ git pull http://kernel.org/pub/scm/linux/kernel/git/$u/$tree
$ git pull rsync://kernel.org/pub/scm/linux/kernel/git/$u/$tree
unless the downloader has already fetched from Linus'
repository, this will not work.
* In the case of rsync transport, it would slurp all objects
your repository has, but does not get objects from Linus'
repository. Also, rsync will overwrite the
objects/info/alternates file the downloader has in his
repository with what you have in your repository, which is
not what we want.