When the given path contains '..' then git-clean incorrectly printed names
of files. This patch changes cmd_clean to use quote_path_relative().
Also, "failed to remove ..." message used absolutely path, but not it is
corrected to use relative path.
Signed-off-by: Dmitry Potapov <dpotapov@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>