builtin-fetch: add --dry-run option Teach fetch --dry-run as users of "git remote prune" switching to "git fetch --prune" may expect it. Unfortunately OPT__DRY_RUN() cannot be used as fetch already uses "-n" for something else. Signed-off-by: Jay Soffian <jaysoffian@gmail.com> Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>