git-checkout: allow "checkout HEAD -- path"
git-checkout: allow "checkout HEAD -- path"

Even though -- is redundant in this case, we should allow it to prevent
confusion.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git