Merge branch 'kb/preload-index-more'

Use preloadindex in more places, which has a nice speedup on systems
with slow stat calls (and even on Linux).

* kb/preload-index-more:
  update-index/diff-index: use core.preloadindex to improve performance

builtin/update-index.c

@@ -593,6 +593,7 @@ struct refresh_params {
 static int refresh(struct refresh_params *o, unsigned int flag)
 {
 	setup_work_tree();
+	read_cache_preload(NULL);
 	*o->has_errors |= refresh_cache(o->flags | flag);
 	return 0;
 }