[Bug] Custom git-dir directory shouldn't be listed as “untracked”

[Nicolas Cuillery <nicolas.cuillery@xxxxxxxxx>]

Hi, I want to create a local repository with a custom dir name instead
of ".git", I used the env vars GIT_DIR and WORK_TREE:
>export GIT_DIR=".customgitdir"
>export GIT_WORK_TREE="."

Then I created a repo in an empty directory:
>$ git init
>Initialized empty Git repository in XXXXXXXXX/.customgitdir/

Then I ran git status:
>$ git status
>On branch master
>
>Initial commit
>
>Untracked files:
>  (use "git add <file>..." to include in what will be committed)
>
>    .customgitdir/
>
>nothing added to commit but untracked files present (use "git add" to track)

The local repo directory listed as "untracked files" which is a
problem when using "git add ." afterwards.

When using the default directory ".git", it logically doesn't appear
in the "git status" command's output. Don't you think it should be the
same when using a custom dir name ?

Git version 2.6.4 on MacOSX 10.11

Regards,
Nicolas