Merge branch 'ds/sparse-index-protections'

Builds on top of the sparse-index infrastructure to mark operations
that are not ready to mark with the sparse index, causing them to
fall back on fully-populated index that they always have worked with.

* ds/sparse-index-protections: (47 commits)
  name-hash: use expand_to_path()
  sparse-index: expand_to_path()
  name-hash: don't add directories to name_hash
  revision: ensure full index
  resolve-undo: ensure full index
  read-cache: ensure full index
  pathspec: ensure full index
  merge-recursive: ensure full index
  entry: ensure full index
  dir: ensure full index
  update-index: ensure full index
  stash: ensure full index
  rm: ensure full index
  merge-index: ensure full index
  ls-files: ensure full index
  grep: ensure full index
  fsck: ensure full index
  difftool: ensure full index
  commit: ensure full index
  checkout: ensure full index
  ...

entry.c

@@ -423,6 +423,8 @@ static void mark_colliding_entries(const struct checkout *state,
 
 	ce->ce_flags |= CE_MATCHED;
 
+	/* TODO: audit for interaction with sparse-index. */
+	ensure_full_index(state->istate);
 	for (i = 0; i < state->istate->cache_nr; i++) {
 		struct cache_entry *dup = state->istate->cache[i];