When you have "t" directory that is marked as ignored in the top-level
.gitignore file (or $GIT_DIR/info/exclude), running
$ git ls-files -o --exclude-standard
from the top-level correctly excludes files in "t" directory, but
any of the following:
$ git ls-files -o --exclude-standard t/
$ cd t && git ls-files -o --exclude-standard
would show untracked files in that directory.
Signed-off-by: Junio C Hamano <gitster@pobox.com>