Merge branch 'sj/untracked-files-in-submodule-directory-is-not-dirty'

"git diff" showed a submodule working tree with untracked cruft as
"Submodule commit <objectname>-dirty", but a natural expectation is
that the "-dirty" indicator would align with "git describe --dirty",
which does not consider having untracked files in the working tree
as source of dirtiness.  The inconsistency has been fixed.

* sj/untracked-files-in-submodule-directory-is-not-dirty:
  diff: do not show submodule with untracked files as "-dirty"

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge

diff --cc submodule.c
Simple merge

diff --cc t/t3701-add-interactive.sh
Simple merge

diff --cc wt-status.c
Simple merge