submodule.*.ignore and diff.ignoresubmodules are used to ignore all
submodule changes in "diff" output, but it can be confusing to
apply these configuration values to status and commit.

This is a backward-incompatible change, but should be so in a good
way (aka bugfix).

* jl/status-added-submodule-is-never-ignored:
  commit -m: commit staged submodules regardless of ignore config
  status/commit: show staged submodules regardless of ignore config