bisect: avoid using the rev_info flag leak_pending

bisect: avoid using the rev_info flag leak_pending

The leak_pending flag is so awkward to use that multiple comments had to
be added around each occurrence.  We only use it for remembering the
commits whose marks we have to clear after checking if all of the good
ones are ancestors of the bad one.  This is easy, though: We need to do
that for the bad and good commits, of course.

Let check_good_are_ancestors_of_bad() create and own the array of bad
and good commits, and use it to clear the commit marks as well.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>