status: do not get confused by submodules in excluded directories

status: do not get confused by submodules in excluded directories

We meticulously pass the `exclude` flag to the `treat_directory()`
function so that we can indicate that files in it are excluded rather
than untracked when recursing.

But we did not yet treat submodules the same way.

Because of that, `git status --ignored --untracked` with a submodule
`submodule` in a gitignored `tracked/` would show the submodule in the
"Untracked files" section, e.g.

	On branch master
	Untracked files:
	  (use "git add <file>..." to include in what will be committed)

		tracked/submodule/

	Ignored files:
	  (use "git add -f <file>..." to include in what will be committed)

		tracked/submodule/initial.t

Instead, we would want it to show the submodule in the "Ignored files"
section:

	On branch master
	Ignored files:
	  (use "git add -f <file>..." to include in what will be committed)

		tracked/submodule/

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>