Merge branch 'mg/submodule-status-from-a-subdirectory'

"git submodule status" that is run from a subdirectory of the
superproject did not work well, which has been corrected.

* mg/submodule-status-from-a-subdirectory:
  submodule: fix 'submodule status' when called from a subdirectory

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

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