git add <single file> and git add <list of files> behave differentely for ignored files

Hello,

I reported this issue on the git-user mailing list and they redirected me here.

The problem I have observed is that with a ignored path `git add <single file>` behaves differently then `git add <list of files>`.

I my git/info/excludes file i have

/COM/config !COM/config/Project.gny

The file COM/config/Project.gny has already been added to the repository via `git add -f`.

When doing

    git add -- COM/config/Projec.gny

git will not complain but when doing

    git add -- COM/config/Project.gny otherfiles.c

it will report:

    The following paths are ignored by one of your .gitignore files:
    COM/config
    Use -f if you really want to add them.
    fatal: no files added

This odd behaviour is also present in `git check-ignore`.

Before adding the file `git check-ignore` correctly reports the file as ignored. After having added it via `git add -f` it won't report it as ignored anymore.

Even if not a bug this behaviour is inconsistent and might want to be addressed as it makes scripting a little bit harder.

Thank you.