Trailers passed to the parse_trailer() function often have
a trailing newline. When erroring out, we should display
the invalid trailer properly, that means without any
trailing newline.
Helped-by: Junio C Hamano <gitster@pobox.com> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Christian Couder <chriscool@tuxfamily.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>