Merge branch 'lx/submodule-clear-variables'

The "git submodule" command did not initialize a few variables it
internally uses and was affected by variable settings leaked from
the environment.

* lx/submodule-clear-variables:
  git-submodule.sh: setup uninitialized variables

git-submodule.sh

@@ -48,6 +48,8 @@ depth=
 progress=
 dissociate=
 single_branch=
+jobs=
+recommend_shallow=
 
 die_if_unmatched ()
 {