[BUG] "git stash -- path" reports wrong unstaged changes

I used "git stash -- path" for the first time today and happened to notice an oddity. If I run:

	git init -q repo
	cd repo
	
	for i in one two; do
		echo content >$i
		git add $i
	done
	git commit -qm base
	
	for i in one two; do
		echo change >$i
	done
	git stash -- one

it says:

  Saved working directory and index state WIP on master: 20cfadf base
  Unstaged changes after reset:
  M	one
  M	two

Even though "one" no longer has unstaged changes.

If I run with GIT_TRACE=1, that message is generated by:

  git reset -- one

which makes sense. At that stage we've just reset the index, but the working tree file still has modifications. In the non-pathspec case we run "git reset --hard", which takes care of the index and the working tree.

It's really "checkout-index" that cleans the working tree, but it doesn't have porcelain finery like an "Unstaged changes" message. I think the patch below would fix it, but I wonder if we can do it in a way that doesn't involve calling diff-files twice.

-Peff

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