builtin-commit.c: add -u as short name for --untracked-files
builtin-commit.c: add -u as short name for --untracked-files

This makes the C code consistent with the documentation and the old shell
code.

Signed-off-by: Sitaram Chamarty <9d65ae67c3bf4d5605b985e8a180f44b838668ef@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

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