Note the caveat where 2.17 is stricter about index validation
potentially causing "could not open directory" warnings when git is
upgraded. See the preceding "dir.c: stop ignoring opendir() error in
open_cached_dir()" change.
This caused some mayhem when I upgraded git to a version with this
series at Booking.com, and other users have doubtless enabled the UC
extension and are in for a surprise when they upgrade. Let's give them
a headsup in the docs.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>