Merge branch 'nd/fix-untracked-cache-invalidation'

Some bugs around "untracked cache" feature have been fixed.

* nd/fix-untracked-cache-invalidation:
dir.c: ignore paths containing .git when invalidating untracked cache
dir.c: stop ignoring opendir() error in open_cached_dir()
dir.c: fix missing dir invalidation in untracked code
dir.c: avoid stat() in valid_cached_dir()
status: add a failing test showing a core.untrackedCache bug

diff --cc dir.c
Simple merge

diff --cc dir.h
Simple merge

diff --cc unpack-trees.c
Simple merge