Merge branch 'sb/submodule-update-try-harder'

"git submodule update" attempts two different kinds of "git fetch" against the upstream repository to grab a commit bound at the submodule's path, but it incorrectly gave up if the first kind (i.e. a normal fetch) failed, making the second "last resort" one (i.e. fetching an exact commit object by object name) ineffective. This has been corrected. * sb/submodule-update-try-harder: git-submodule.sh: try harder to fetch a submodule