Merge branch 'ds/disable-replace-refs' into next

Introduce a mechanism to disable replace refs globally and per
repository.

* ds/disable-replace-refs:
  repository: create read_replace_refs setting
  replace-objects: create wrapper around setting
  repository: create disable_replace_refs()
  pack-bitmap.c: use commit boundary during bitmap traversal
  pack-bitmap.c: extract `fill_in_bitmap()`
  object: add object_array initializer helper function

builtin/commit-graph.c

@@ -325,7 +325,7 @@ int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 
 	git_config(git_default_config, NULL);
 
-	read_replace_refs = 0;
+	disable_replace_refs();
 	save_commit_buffer = 0;
 
 	argc = parse_options(argc, argv, prefix, options,