Merge branch 'mg/maint-submodule-normalize-path' into maint

* mg/maint-submodule-normalize-path:
  git submodule: Fix adding of submodules at paths with ./, .. and //
  git submodule: Add test cases for git submodule add

diff --cc git-submodule.sh
Simple merge

diff --cc t/t7400-submodule-basic.sh
Simple merge