Merge branch 'nd/the-index-final'

Merge branch 'nd/the-index-final'

The assumption to work on the single "in-core index" instance has
been reduced from the library-ish part of the codebase.

* nd/the-index-final:
  cache.h: flip NO_THE_INDEX_COMPATIBILITY_MACROS switch
  read-cache.c: remove the_* from index_has_changes()
  merge-recursive.c: remove implicit dependency on the_repository
  merge-recursive.c: remove implicit dependency on the_index
  sha1-name.c: remove implicit dependency on the_index
  read-cache.c: replace update_index_if_able with repo_&
  read-cache.c: kill read_index()
  checkout: avoid the_index when possible
  repository.c: replace hold_locked_index() with repo_hold_locked_index()
  notes-utils.c: remove the_repository references
  grep: use grep_opt->repo instead of explict repo argument