Merge branch 'sb/show-diff-for-submodule-in-diff-fix'

"git diff --submodule=diff" learned to work better in a project
with a submodule that in turn has its own submodules.

* sb/show-diff-for-submodule-in-diff-fix:
diff: submodule inline diff to initialize env array.

diff --cc submodule.c
Simple merge