Merge branch 'dl/submodule-set-url'

"git submodule" learned a subcommand "set-url".

* dl/submodule-set-url:
  submodule: teach set-url subcommand

diff --cc Documentation/git-submodule.txt
Simple merge

diff --cc contrib/completion/git-completion.bash
Simple merge

diff --cc git-submodule.sh
Simple merge