Merge branch 'nd/invalidate-i-t-a-cache-tree'

After "git add -N" and then writing a tree object out of the
index, the cache-tree data structure got corrupted.

* nd/invalidate-i-t-a-cache-tree:
  cache-tree: invalidate i-t-a paths after generating trees
  cache-tree: fix writing cache-tree when CE_REMOVE is present
  cache-tree: replace "for" loops in update_one with "while" loops
  cache-tree: remove dead i-t-a code in verify_cache()