Commit 758e915 made sq_quote_next static, removing it from
quote.h. However, it forgot to update the related comment,
making it appear as a confusing description of sq_quote_to_argv.
Let's remove the crufty bits, and elaborate more on sq_quote_to_argv.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>