Merge branch 'js/defeat-ignore-submodules-config-with-explicit-addition'

Even when diff.ignoreSubmodules tells us to ignore submodule
changes, "git commit" with an index that already records changes to
submodules should include the submodule changes in the resulting
commit, but it did not.

* js/defeat-ignore-submodules-config-with-explicit-addition:
  diff-lib: honor override_submodule_config flag bit