use parse_object_or_die instead of die("bad object")

use parse_object_or_die instead of die("bad object")

Some call-sites do:

  o = parse_object(sha1);
  if (!o)
	  die("bad object %s", some_name);

We can now handle that as a one-liner, and get more
consistent output.

In the third case of this patch, it looks like we are losing
information, as the existing message also outputs the sha1
hex; however, parse_object will already have written a more
specific complaint about the sha1, so there is no point in
repeating it here.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>