Merge branch 'jc/cache-tree'

* jc/cache-tree:
  Avoid "diff-index --cached" optimization under --find-copies-harder
  Optimize "diff-index --cached" using cache-tree
  t4007: modernize the style
  cache-tree.c::cache_tree_find(): simplify internal API
  write-tree --ignore-cache-tree

diff --cc diff-lib.c
Simple merge