t0020: fix ignored exit code inside loops

t0020: fix ignored exit code inside loops

A loop like:

  for f in one two; do
	  something $f ||
	  break
  done

will correctly break out of the loop when we see a failure
of one item, but the resulting exit code will always be
zero. We can fix that by putting the loop into a function or
subshell, but in this case it is simpler still to just
unroll the loop. We do add a helper function, which
hopefully makes the end result even more readable (in
addition to being shorter).

Reported-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>