Merge branch 'sb/submodule-fetch-nontip'

When "git submodule update" did not result in fetching the commit object in the submodule that is referenced by the superproject, the command learned to retry another fetch, specifically asking for that commit that may not be connected to the refs it usually fetches. * sb/submodule-fetch-nontip: submodule: try harder to fetch needed sha1 by direct fetching sha1