Merge branch 'es/recursive-single-branch-clone'

"git clone --recurse-submodules --single-branch" now uses the same
single-branch option when cloning the submodules.

* es/recursive-single-branch-clone:
  clone: pass --single-branch during --recurse-submodules
  submodule--helper: use C99 named initializer

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

diff --cc builtin/clone.c
Simple merge

diff --cc builtin/submodule--helper.c
Simple merge

diff --cc git-submodule.sh
Simple merge