Merge branch 'jc/attr-source-tree'

"git --attr-source=<tree> cmd $args" is a new way to have any
command to read attributes not from the working tree but from the
given tree object.

* jc/attr-source-tree:
  attr: teach "--attr-source=<tree>" global option to "git"

archive.c

@@ -130,7 +130,7 @@ static const struct attr_check *get_archive_attrs(struct index_state *istate,
 	static struct attr_check *check;
 	if (!check)
 		check = attr_check_initl("export-ignore", "export-subst", NULL);
-	git_check_attr(istate, NULL, path, check);
+	git_check_attr(istate, path, check);
 	return check;
 }