Merge branch 'pb/recurse-submodules-fix'

Fix "git checkout --recurse-submodules" of a nested submodule hierarchy. * pb/recurse-submodules-fix: t/lib-submodule-update: add test removing nested submodules unpack-trees: check for missing submodule directory in merged_entry unpack-trees: remove outdated description for verify_clean_submodule t/lib-submodule-update: move a test to the right section t/lib-submodule-update: remove outdated test description t7112: remove mention of KNOWN_FAILURE_SUBMODULE_RECURSIVE_NESTED