Merge branch 'jl/submodule-diff-dirtiness'

* jl/submodule-diff-dirtiness:
git status: ignoring untracked files must apply to submodules too
git status: Fix false positive "new commits" output for dirty submodules
Refactor dirty submodule detection in diff-lib.c
git status: Show detailed dirty status of submodules in long format
git diff --submodule: Show detailed dirty status of submodules

diff --cc diff-lib.c
Simple merge

diff --cc diff.c
Simple merge

diff --cc wt-status.c
Simple merge