Merge branch 'lt/in-core-index'

Merge branch 'lt/in-core-index'

* lt/in-core-index:
  lazy index hashing
  Create pathname-based hash-table lookup into index
  read-cache.c: introduce is_racy_timestamp() helper
  read-cache.c: fix a couple more CE_REMOVE conversion
  Also use unpack_trees() in do_diff_cache()
  Make run_diff_index() use unpack_trees(), not read_tree()
  Avoid running lstat(2) on the same cache entry.
  index: be careful when handling long names
  Make on-disk index representation separate from in-core one