Historically, "git status" needed to prefix each output line with '#' so
that the output could be added as comment to the commit message. This
prefix comment has no real purpose when "git status" is ran from the
command-line, and this may distract users from the real content.

Disable this prefix comment by default, and make it re-activable for
users needing backward compatibility with status.displayCommentPrefix.

Obviously, "git commit" ignores status.displayCommentPrefix and keeps the
comment unconditionnaly when writing to COMMIT_EDITMSG (but not when
writing to stdout for an error message or with --dry-run).
Signed-off-by: NMatthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>