Fix 'git add' with .gitignore

Fix 'git add' with .gitignore

When '*.ig' is ignored, and you have two files f.ig and d.ig/foo
in the working tree,

	$ git add .

correctly ignored f.ig but failed to ignore d.ig/foo.  This was
caused by a thinko in an earlier commit 4888c534, when we tried
to allow adding otherwise ignored files.

After reverting that commit, this takes a much simpler approach.
When we have an unmatched pathspec that talks about an existing
pathname, we know it is an ignored path the user tried to add,
so we include it in the set of paths directory walker returned.

This does not let you say "git add -f D" on an ignored directory
D and add everything under D.  People can submit a patch to
further allow it if they want to, but I think it is a saner
behaviour to require explicit paths to be spelled out in such a
case.

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