We correctly handle completion items with spaces just fine,
since we pass the lists around with newline delimiters.
However, we do not handle filenames with shell
metacharacters, as "compgen -W" performs expansion on the
list we give it.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>