git-checkout: allow pathspec to recover lost working tree directory

git-checkout: allow pathspec to recover lost working tree directory

It is often wanted on the #git channel that this were to work to
recover removed directory:

	rm -fr Documentation
	git checkout -- Documentation
	git checkout HEAD -- Documentation ;# alternatively

Now it does.

Signed-off-by: Junio C Hamano <junkio@cox.net>