Merge branch 'jc/ls-files-i-dir'

Merge branch 'jc/ls-files-i-dir'

"git ls-files --exclude=t -i" did not consider anything under t/
as excluded, as it did not pay attention to exclusion of leading
paths while walking the index.  Other two users of excluded() are
also updated.

* jc/ls-files-i-dir:
  dir.c: make excluded() file scope static
  unpack-trees.c: use path_excluded() in check_ok_to_remove()
  builtin/add.c: use path_excluded()
  path_excluded(): update API to less cache-entry centric
  ls-files -i: micro-optimize path_excluded()
  ls-files -i: pay attention to exclusion of leading paths