Merge branch 'jk/allow-fetch-onelevel-refname' into maint

"git clone" would fail to clone from a repository that has a ref directly under "refs/", e.g. "refs/stash", because different validation paths do different things on such a refname. Loosen the client side's validation to allow such a ref. * jk/allow-fetch-onelevel-refname: fetch-pack: do not filter out one-level refs