Updating submodules from the upstream did not work well when
submodule's HEAD is detached, which has been improved.
* jk/submodule-remote-lookup-cleanup:
submodule: look up remotes by URL first
submodule: move get_default_remote_submodule()
submodule--helper: improve logic for fallback remote name
remote: remove the_repository from some functions
dir: move starts_with_dot(_dot)_slash to dir.h
remote: fix tear down of struct remote
remote: remove branch->merge_name and fix branch_release()